feat: 跨实例同步移植 WIP 检查点（第1轮+2a+2b+synced_servers）

从 Axolotl 移植跨实例同步子系统，当前进度： - 第1轮：synced_options/files.rs + mod.rs 骨架，state 层补齐 SyncedOption/InstanceSyncedOptions/CanonicalValue/GameOptionKind 等 - 2a：game_options 的 api_types/options_file/catalog(10文件) - 2b：game_options 除 resource_pack_options/local_settings_editor 外的全部（settings_editor/write_shared_settings/fullscreen/launch_overrides/instance_support/read_instance_changes/pack_updates/source_selection + locales/5文件）；State 补 synced_options_lock/game_locale_indexer/lock_synced_options - synced_servers：6 文件全部搬入 - 35+20 处 sqlx::query! 宏改写为非宏 query+bind 已知未完成：synced_servers::operations 依赖 synced_options::instance_option_supported（属 orchestration，第5轮），当前编译不通。
2026-10-03 22:18:37 +08:00
1 parent 5a289c3a15
commit ed61a5942c
@@ -16,6 +16,8 @@ mod run;
 mod screenshot_groups;
 mod screenshots;
 mod upgrade;
+pub(crate) mod synced_options;
+pub(crate) mod synced_servers;

 pub use self::backup::{
    BackupDeleteSummary, BackupExclusion, BackupExclusionKind, BackupOperation,
@@ -0,0 +1,338 @@
+use crate::state::{InstanceInstallStage, InstanceMetadata, SyncedOption};
+use crate::util::io;
+use crate::{ErrorKind, State};
+use quartz_nbt::NbtCompound;
+use sha1_smol::Sha1;
+use std::io::Cursor;
+use std::path::{Path, PathBuf};
+
+pub(in crate::api::instance) struct SyncCheckpoint {
+    pub expected_sha1: String,
+    pub merge_base: Option<Vec<u8>>,
+    pub source_revision: i64,
+    pub status: CheckpointStatus,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub(in crate::api::instance) enum CheckpointStatus {
+    Pending,
+    Ready,
+}
+
+impl CheckpointStatus {
+    fn from_str(value: &str) -> Option<Self> {
+        match value {
+            "pending" => Some(Self::Pending),
+            "ready" => Some(Self::Ready),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub(in crate::api::instance) enum LinkMode {
+    Symbolic,
+    #[cfg(windows)]
+    Hard,
+    #[cfg(windows)]
+    Copy,
+}
+
+impl LinkMode {
+    fn as_str(self) -> &'static str {
+        match self {
+            Self::Symbolic => "symbolic",
+            #[cfg(windows)]
+            Self::Hard => "hard",
+            #[cfg(windows)]
+            Self::Copy => "copy",
+        }
+    }
+}
+
+pub(in crate::api::instance) fn safe_instance_id(instance_id: &str) -> String {
+    instance_id.replace([':', '/', '\\'], "_")
+}
+
+pub(crate) fn instance_game_dir(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<PathBuf> {
+    crate::state::instances::commands::instance_content_root(
+        &state.directories,
+        &metadata.instance,
+    )
+}
+
+pub(crate) fn synced_options_path(state: &State) -> PathBuf {
+    state.directories.synced_options_dir()
+}
+
+pub(in crate::api::instance) fn sync_files_are_protected(
+    metadata: &InstanceMetadata,
+) -> bool {
+    matches!(
+        metadata.instance.install_stage,
+        InstanceInstallStage::MinecraftInstalling
+            | InstanceInstallStage::PackInstalling
+    )
+}
+
+pub(in crate::api::instance) async fn instance_is_running(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<bool> {
+    crate::state::instance_has_running_process(&metadata.instance.id, state)
+        .await
+}
+
+pub(in crate::api::instance) fn option_can_apply_while_running(
+    option: SyncedOption,
+) -> bool {
+    matches!(
+        option,
+        SyncedOption::GameOptions
+            | SyncedOption::Screenshots
+            | SyncedOption::ResourcePacks
+    )
+}
+
+pub(in crate::api::instance) fn instance_option_enabled(
+    metadata: &InstanceMetadata,
+    option: SyncedOption,
+) -> bool {
+    match option {
+        SyncedOption::GameOptions => metadata.synced_options.game_options,
+        SyncedOption::CommandHistory => metadata.synced_options.command_history,
+        SyncedOption::MultiplayerServers => {
+            metadata.synced_options.multiplayer_servers
+        }
+        SyncedOption::CreativeHotbars => {
+            metadata.synced_options.creative_hotbars
+        }
+        SyncedOption::Screenshots => metadata.synced_options.screenshots,
+        SyncedOption::ResourcePacks => metadata.synced_options.resource_packs,
+        SyncedOption::DataPacks => metadata.synced_options.data_packs,
+    }
+}
+
+pub(in crate::api::instance) async fn ensure_link(
+    source: &Path,
+    target: &Path,
+) -> crate::Result<LinkMode> {
+    if let Some(parent) = target.parent() {
+        io::create_dir_all(parent).await?;
+    }
+    if tokio::fs::symlink_metadata(target)
+        .await
+        .is_ok_and(|metadata| metadata.file_type().is_symlink())
+        && tokio::fs::read_link(target)
+            .await
+            .is_ok_and(|current| current == source)
+    {
+        return Ok(LinkMode::Symbolic);
+    }
+    if tokio::fs::symlink_metadata(target).await.is_ok() {
+        io::remove_file(target).await?;
+    }
+
+    #[cfg(unix)]
+    {
+        tokio::fs::symlink(source, target).await?;
+        Ok(LinkMode::Symbolic)
+    }
+    #[cfg(windows)]
+    {
+        if tokio::fs::symlink_file(source, target).await.is_ok() {
+            return Ok(LinkMode::Symbolic);
+        }
+        if tokio::fs::hard_link(source, target).await.is_ok() {
+            return Ok(LinkMode::Hard);
+        }
+        io::copy(source, target).await?;
+        Ok(LinkMode::Copy)
+    }
+}
+
+pub(in crate::api::instance) async fn detach_link(
+    source: &Path,
+    target: &Path,
+) -> crate::Result<()> {
+    let target_metadata = tokio::fs::symlink_metadata(target).await.ok();
+    let contents = if target_metadata.is_some() && target.exists() {
+        Some(io::read(target).await?)
+    } else if source.exists() {
+        Some(io::read(source).await?)
+    } else {
+        None
+    };
+    if target_metadata.is_some() {
+        io::remove_file(target).await?;
+    }
+    if let Some(contents) = contents {
+        io::write(target, contents).await?;
+    }
+    Ok(())
+}
+
+pub(in crate::api::instance) async fn begin_checkpoint(
+    instance_id: &str,
+    option: SyncedOption,
+    variant: &str,
+    expected_sha1: &str,
+    merge_base: Option<&[u8]>,
+    source_revision: i64,
+    state: &State,
+) -> crate::Result<()> {
+    let option_name = option.as_str();
+    sqlx::query(
+        "
+		INSERT INTO instance_sync_checkpoints
+			(instance_id, feature, variant, expected_sha1, merge_base,
+			 source_revision, status, link_mode)
+		VALUES (?, ?, ?, ?, ?, ?, 'pending', NULL)
+		ON CONFLICT(instance_id, feature, variant) DO UPDATE SET
+			expected_sha1 = excluded.expected_sha1,
+			merge_base = excluded.merge_base,
+			source_revision = excluded.source_revision,
+			status = 'pending',
+			link_mode = NULL
+		",
+    )
+    .bind(instance_id)
+    .bind(option_name)
+    .bind(variant)
+    .bind(expected_sha1)
+    .bind(merge_base)
+    .bind(source_revision)
+    .execute(&state.pool)
+    .await?;
+    Ok(())
+}
+
+pub(in crate::api::instance) async fn finish_checkpoint(
+    instance_id: &str,
+    option: SyncedOption,
+    variant: &str,
+    mode: LinkMode,
+    state: &State,
+) -> crate::Result<()> {
+    let option_name = option.as_str();
+    let link_mode = mode.as_str();
+    sqlx::query(
+        "
+		UPDATE instance_sync_checkpoints
+		SET status = 'ready', link_mode = ?
+		WHERE instance_id = ? AND feature = ? AND variant = ?
+		",
+    )
+    .bind(link_mode)
+    .bind(instance_id)
+    .bind(option_name)
+    .bind(variant)
+    .execute(&state.pool)
+    .await?;
+    Ok(())
+}
+
+pub(in crate::api::instance) async fn finish_plain_checkpoint(
+    instance_id: &str,
+    option: SyncedOption,
+    variant: &str,
+    state: &State,
+) -> crate::Result<()> {
+    let option_name = option.as_str();
+    sqlx::query(
+        "
+		UPDATE instance_sync_checkpoints
+		SET status = 'ready', link_mode = NULL
+		WHERE instance_id = ? AND feature = ? AND variant = ?
+		",
+    )
+    .bind(instance_id)
+    .bind(option_name)
+    .bind(variant)
+    .execute(&state.pool)
+    .await?;
+    Ok(())
+}
+
+pub(in crate::api::instance) async fn checkpoint(
+    instance_id: &str,
+    option: SyncedOption,
+    variant: &str,
+    state: &State,
+) -> crate::Result<Option<SyncCheckpoint>> {
+    let option_name = option.as_str();
+    let row = sqlx::query(
+        r#"
+		SELECT expected_sha1, merge_base, source_revision, status
+		FROM instance_sync_checkpoints
+		WHERE instance_id = ? AND feature = ? AND variant = ?
+		"#,
+    )
+    .bind(instance_id)
+    .bind(option_name)
+    .bind(variant)
+    .fetch_optional(&state.pool)
+    .await?;
+    use sqlx::Row;
+    row.map(|row| {
+        let status: String = row.get("status");
+        Ok(SyncCheckpoint {
+            expected_sha1: row.get("expected_sha1"),
+            merge_base: row.get("merge_base"),
+            source_revision: row.get("source_revision"),
+            status: CheckpointStatus::from_str(&status).ok_or_else(|| {
+                ErrorKind::InputError(format!(
+                    "Unknown sync checkpoint status {status}"
+                ))
+            })?,
+        })
+    })
+    .transpose()
+}
+
+pub(in crate::api::instance) async fn sha1_file(
+    path: &Path,
+) -> crate::Result<String> {
+    Ok(Sha1::from(io::read(path).await?).digest().to_string())
+}
+
+pub(in crate::api::instance) fn sha1_bytes(bytes: &[u8]) -> String {
+    Sha1::from(bytes).digest().to_string()
+}
+
+pub(in crate::api::instance) async fn read_nbt_file(
+    path: &Path,
+) -> crate::Result<NbtCompound> {
+    let bytes = io::read(path).await?;
+    let (root, _) = quartz_nbt::io::read_nbt(
+        &mut Cursor::new(bytes),
+        quartz_nbt::io::Flavor::Uncompressed,
+    )?;
+    Ok(root)
+}
+
+pub(in crate::api::instance) fn nbt_to_bytes(
+    root: &NbtCompound,
+) -> crate::Result<Vec<u8>> {
+    let mut bytes = Vec::new();
+    quartz_nbt::io::write_nbt(
+        &mut bytes,
+        None,
+        root,
+        quartz_nbt::io::Flavor::Uncompressed,
+    )?;
+    Ok(bytes)
+}
+
+pub(in crate::api::instance) fn nbt_from_bytes(
+    bytes: Vec<u8>,
+) -> crate::Result<NbtCompound> {
+    let (root, _) = quartz_nbt::io::read_nbt(
+        &mut Cursor::new(bytes),
+        quartz_nbt::io::Flavor::Uncompressed,
+    )?;
+    Ok(root)
+}
@@ -0,0 +1,203 @@
+use crate::state::{CanonicalValue, GameOptionKind};
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum GameOptionsSourceIssue {
+    InstallingOrUpdating,
+    UnsupportedVersion,
+    MissingOptionsFile,
+    NoSyncableSettings,
+    UnreadableOptionsFile,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct GameOptionsSourceCandidate {
+    pub source_id: String,
+    pub instance_id: String,
+    pub name: String,
+    pub icon_path: Option<String>,
+    pub game_version: Option<String>,
+    pub eligible: bool,
+    pub disabled_reason: Option<GameOptionsSourceIssue>,
+    pub recognized_setting_count: u32,
+    pub custom_setting_count: u32,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct GameSettingCategory {
+    pub id: String,
+    pub is_custom: bool,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct GameOptionEditorDefinition {
+    #[serde(rename = "type")]
+    pub type_: String,
+    pub min: Option<f64>,
+    pub max: Option<f64>,
+    pub step: Option<f64>,
+    pub unit: Option<String>,
+    pub choices: Vec<GameOptionEditorChoice>,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct GameOptionEditorChoice {
+    pub value: String,
+}
+
+#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum GameOptionCompatibilityStatus {
+    Ready,
+    Deferred,
+    WaitingForFile,
+    WaitingForBase,
+    NotAvailable,
+    UnsupportedValue,
+    Unmappable,
+    CatalogUncovered,
+    Controlled,
+    Degraded,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum GameOptionMappingKind {
+    Direct,
+    Legacy,
+    Migrated,
+    Lossless,
+    Lossy,
+}
+
+#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum GameOptionCompatibilityReason {
+    LauncherControlled,
+    CatalogUncovered,
+    InspectionFailed,
+    WaitingForOptionsFile,
+    UnsupportedValue,
+    MigratesOnWrite,
+    WaitingForCompatibleBase,
+    MissingSetting,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct GameOptionCompatibilityBucket {
+    pub instance_count: u32,
+    pub write_keys: Vec<String>,
+    pub eventual_keys: Vec<String>,
+    pub game_versions: Vec<String>,
+    pub status: GameOptionCompatibilityStatus,
+    pub mapping: Option<GameOptionMappingKind>,
+    pub reason: Option<GameOptionCompatibilityReason>,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct GameOptionCompatibility {
+    pub total_participating: u32,
+    pub will_receive: u32,
+    pub write_now: u32,
+    pub left_local: u32,
+    pub buckets: Vec<GameOptionCompatibilityBucket>,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum GameOptionValueState {
+    Canonical,
+    UniformLocal,
+    Mixed,
+    Unset,
+    Invalid,
+}
+
+#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum GameOptionValidationIssue {
+    MissingValue,
+    NoCompatibleInstances,
+    InvalidValue,
+    ChangedSinceOpened,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct EditableGameSetting {
+    pub option_id: String,
+    pub category_id: String,
+    pub kind: GameOptionKind,
+    pub raw_key: Option<String>,
+    pub sync_enabled: bool,
+    pub canonical_value: Option<CanonicalValue>,
+    pub value_state: GameOptionValueState,
+    pub option_revision: u64,
+    pub editor: GameOptionEditorDefinition,
+    pub compatibility: GameOptionCompatibility,
+    pub validation_error: Option<GameOptionValidationIssue>,
+    pub controlled: bool,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct GameSettingsEditorState {
+    pub summary_revision: String,
+    pub canonical_revision: u64,
+    pub catalog_revision: u32,
+    pub total_participating: u32,
+    pub categories: Vec<GameSettingCategory>,
+    pub settings: Vec<EditableGameSetting>,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct UpdateGameSettingsRequest {
+    pub expected_summary_revision: String,
+    pub expected_canonical_revision: u64,
+    pub expected_catalog_revision: u32,
+    pub changes: Vec<GameSettingChange>,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct GameSettingChange {
+    pub option_id: String,
+    pub base_option_revision: u64,
+    pub sync_enabled: Option<bool>,
+    #[serde(
+        default,
+        with = "serde_with::rust::double_option",
+        skip_serializing_if = "Option::is_none"
+    )]
+    pub canonical_value: Option<Option<CanonicalValue>>,
+}
+
+#[derive(Clone, Debug, Default, Serialize, Deserialize)]
+pub struct SaveGameSettingsResult {
+    pub state: Option<GameSettingsEditorState>,
+    pub applied: u32,
+    pub migrated: u32,
+    pub deferred: u32,
+    pub unsupported: u32,
+    pub failed: u32,
+    pub conflicts: Vec<String>,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub(super) enum SyncOutcome {
+    Applied,
+    Migrated,
+    Unchanged,
+    Deferred,
+    WaitingForFile,
+}
+
+pub(super) fn canonical_values_equal(
+    left: &CanonicalValue,
+    right: &CanonicalValue,
+) -> bool {
+    match (left, right) {
+        (CanonicalValue::Decimal(left), CanonicalValue::Decimal(right)) => {
+            left.parse::<f64>().ok() == right.parse::<f64>().ok()
+        }
+        _ => left == right,
+    }
+}
@@ -0,0 +1,207 @@
+use super::{
+    BOOL, SettingEditor, SupportedSetting, UNIT_INTERVAL, ValueEncoding,
+    ranged_setting, version_changes, versioned_setting,
+};
+
+const NARRATOR: &[&str] = &["0", "1", "2", "3"];
+
+pub(super) const SETTINGS: &[SupportedSetting] = &[
+    ranged_setting(
+        "narrator",
+        &["narrator"],
+        "1.12",
+        "26.3",
+        "accessibility",
+        true,
+        SettingEditor::Enum(NARRATOR),
+        ValueEncoding::Enum(NARRATOR),
+    ),
+    ranged_setting(
+        "subtitles",
+        &["showSubtitles"],
+        "1.9",
+        "26.3",
+        "accessibility",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "high_contrast",
+        &["highContrast"],
+        "1.19.4",
+        "26.3",
+        "accessibility",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "dark_splash",
+        &["darkMojangStudiosBackground"],
+        "1.17",
+        "26.3",
+        "accessibility",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "notification_time",
+        &["notificationDisplayTime"],
+        "1.19.4",
+        "26.3",
+        "accessibility",
+        true,
+        SettingEditor::Decimal {
+            min: 0.5,
+            max: 10.0,
+            step: 0.5,
+            unit: Some("multiplier"),
+        },
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "fov_effects",
+        &["fovEffectScale"],
+        "1.16.2",
+        "26.3",
+        "accessibility",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "screen_effects",
+        &["screenEffectScale"],
+        "1.16.2",
+        "26.3",
+        "accessibility",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "darkness_pulsing",
+        &["darknessEffectScale"],
+        "1.19",
+        "26.3",
+        "accessibility",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "damage_tilt",
+        &["damageTiltStrength"],
+        "1.19.4",
+        "26.3",
+        "accessibility",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "glint_speed",
+        &["glintSpeed"],
+        "1.19.4",
+        "26.3",
+        "accessibility",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "glint_strength",
+        &["glintStrength"],
+        "1.19.4",
+        "26.3",
+        "accessibility",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "hide_lightning_flashes",
+        &["hideLightningFlashes"],
+        "1.18",
+        "26.3",
+        "accessibility",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "hide_splash_texts",
+        &["hideSplashTexts"],
+        "1.20.3",
+        "26.3",
+        "accessibility",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "high_contrast_outline",
+        &["highContrastBlockOutline"],
+        "1.21.2",
+        "26.3",
+        "accessibility",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "narrator_hotkey",
+        &["narratorHotkey"],
+        "1.20.2",
+        "26.3",
+        "accessibility",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "autosave_indicator",
+        &["showAutosaveIndicator"],
+        "1.18",
+        "26.3",
+        "accessibility",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "panorama_speed",
+        &["panoramaScrollSpeed"],
+        "1.19.3",
+        "26.3",
+        "accessibility",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    versioned_setting(
+        "menu_background_blur",
+        &["menuBackgroundBlurriness"],
+        version_changes::MENU_BACKGROUND_BLUR_KEYS,
+        "accessibility",
+        true,
+        SettingEditor::Integer {
+            min: 0,
+            max: 10,
+            step: 1,
+        },
+        ValueEncoding::MenuBackgroundBlur,
+    ),
+    ranged_setting(
+        "rotate_with_minecart",
+        &["rotateWithMinecart"],
+        "1.21.2",
+        "26.3",
+        "accessibility",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+];
@@ -0,0 +1,194 @@
+use super::{
+    BOOL, SettingEditor, SupportedSetting, UNIT_INTERVAL, ValueEncoding,
+    ranged_setting, version_changes, versioned_setting,
+};
+
+const VISIBILITY: &[&str] = &["0", "1", "2"];
+const CHAT_PREVIEW: &[&str] = &["0", "1", "2"];
+
+pub(super) const SETTINGS: &[SupportedSetting] = &[
+    ranged_setting(
+        "chat_visibility",
+        &["chatVisibility"],
+        "1.3.1",
+        "26.3",
+        "chat",
+        true,
+        SettingEditor::Enum(VISIBILITY),
+        ValueEncoding::Enum(VISIBILITY),
+    ),
+    ranged_setting(
+        "chat_colors",
+        &["chatColors"],
+        "1.3.1",
+        "26.3",
+        "chat",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "chat_links",
+        &["chatLinks"],
+        "1.3.1",
+        "26.3",
+        "chat",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "chat_links_prompt",
+        &["chatLinksPrompt"],
+        "1.3.1",
+        "26.3",
+        "chat",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "chat_opacity",
+        &["chatOpacity"],
+        "1.3.1",
+        "26.3",
+        "chat",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "chat_scale",
+        &["chatScale"],
+        "1.5.1",
+        "26.3",
+        "chat",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "chat_width",
+        &["chatWidth"],
+        "1.5.1",
+        "26.3",
+        "chat",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "focused_chat_height",
+        &["chatHeightFocused"],
+        "1.5.1",
+        "26.3",
+        "chat",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "unfocused_chat_height",
+        &["chatHeightUnfocused"],
+        "1.5.1",
+        "26.3",
+        "chat",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "chat_line_spacing",
+        &["chatLineSpacing"],
+        "1.16",
+        "26.3",
+        "chat",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "chat_delay",
+        &["chatDelay"],
+        "1.16",
+        "26.3",
+        "chat",
+        true,
+        SettingEditor::Decimal {
+            min: 0.0,
+            max: 6.0,
+            step: 0.1,
+            unit: Some("seconds"),
+        },
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "text_background_opacity",
+        &["textBackgroundOpacity"],
+        "1.14",
+        "26.3",
+        "chat",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "chat_background_only",
+        &["backgroundForChatOnly"],
+        "1.14",
+        "26.3",
+        "chat",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "auto_suggestions",
+        &["autoSuggestions"],
+        "1.13",
+        "26.3",
+        "chat",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "secure_chat_only",
+        &["onlyShowSecureChat"],
+        "1.19",
+        "26.3",
+        "chat",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "save_chat_drafts",
+        &["saveChatDrafts"],
+        "1.21.9",
+        "26.3",
+        "chat",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "hide_matched_names",
+        &["hideMatchedNames"],
+        "1.16.4",
+        "26.3",
+        "chat",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    versioned_setting(
+        "chat_preview",
+        &["chatPreview"],
+        version_changes::CHAT_PREVIEW_KEYS,
+        "chat",
+        true,
+        SettingEditor::Enum(CHAT_PREVIEW),
+        ValueEncoding::ChatPreview,
+    ),
+];
@@ -0,0 +1,413 @@
+use super::{
+    BOOL, SettingEditor, SupportedSetting, ValueEncoding, ranged_setting,
+    setting, version_changes, versioned_setting,
+};
+
+macro_rules! key_setting {
+    ($id:literal, $key:literal, $since:literal, $until:literal) => {
+        ranged_setting(
+            $id,
+            &[$key],
+            $since,
+            $until,
+            "controls",
+            true,
+            SettingEditor::KeyBinding,
+            ValueEncoding::KeyBinding,
+        )
+    };
+}
+
+pub(super) const SETTINGS: &[SupportedSetting] = &[
+    setting(
+        "sensitivity",
+        &["mouseSensitivity"],
+        "controls",
+        true,
+        SettingEditor::Decimal {
+            min: 0.0,
+            max: 1.0,
+            step: 0.005,
+            unit: Some("percent"),
+        },
+        ValueEncoding::Decimal,
+    ),
+    setting(
+        "invert_mouse",
+        &["invertYMouse"],
+        "controls",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "invert_horizontal_mouse",
+        &["invertXMouse"],
+        "1.21.9",
+        "26.3",
+        "controls",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "auto_jump",
+        &["autoJump"],
+        "1.10",
+        "26.3",
+        "controls",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "toggle_crouch",
+        &["toggleCrouch"],
+        "1.15",
+        "26.3",
+        "controls",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "toggle_sprint",
+        &["toggleSprint"],
+        "1.15",
+        "26.3",
+        "controls",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "toggle_attack",
+        &["toggleAttack"],
+        "1.21.9",
+        "26.3",
+        "controls",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "toggle_use",
+        &["toggleUse"],
+        "1.21.9",
+        "26.3",
+        "controls",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "discrete_mouse_scroll",
+        &["discrete_mouse_scroll"],
+        "1.14",
+        "26.3",
+        "controls",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "mouse_wheel_sensitivity",
+        &["mouseWheelSensitivity"],
+        "1.13",
+        "26.3",
+        "controls",
+        true,
+        SettingEditor::UnboundedDecimal,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "raw_mouse_input",
+        &["rawMouseInput"],
+        "1.14.4",
+        "26.2",
+        "controls",
+        false,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "touchscreen",
+        &["touchscreen"],
+        "1.4.4",
+        "26.1.2",
+        "controls",
+        false,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "allow_cursor_changes",
+        &["allowCursorChanges"],
+        "1.21.9",
+        "26.3",
+        "controls",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "sprint_window",
+        &["sprintWindow"],
+        "1.21.9",
+        "26.3",
+        "controls",
+        true,
+        SettingEditor::UnboundedInteger,
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "operator_items_tab",
+        &["operatorItemsTab"],
+        "1.19.3",
+        "26.3",
+        "controls",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "ctrl_click_right_click",
+        &["ctrlClickEmulatesRightClick"],
+        "26.3",
+        "26.3",
+        "controls",
+        false,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "quit_shortcuts",
+        &["quitShortcuts"],
+        "26.3",
+        "26.3",
+        "controls",
+        false,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    key_setting!("key.forward", "key_key.forward", "1.0", "26.3"),
+    key_setting!("key.left", "key_key.left", "1.0", "26.3"),
+    key_setting!("key.back", "key_key.back", "1.0", "26.3"),
+    key_setting!("key.right", "key_key.right", "1.0", "26.3"),
+    key_setting!("key.jump", "key_key.jump", "1.0", "26.3"),
+    key_setting!("key.sneak", "key_key.sneak", "1.0", "26.3"),
+    key_setting!("key.sprint", "key_key.sprint", "1.7.2", "26.3"),
+    key_setting!("key.inventory", "key_key.inventory", "1.0", "26.3"),
+    versioned_setting(
+        "key.swap_offhand",
+        &["key_key.swapOffhand", "key_key.swapHands"],
+        version_changes::SWAP_OFFHAND_KEYS,
+        "controls",
+        true,
+        SettingEditor::KeyBinding,
+        ValueEncoding::KeyBinding,
+    ),
+    key_setting!("key.drop", "key_key.drop", "1.0", "26.3"),
+    key_setting!("key.use", "key_key.use", "1.0", "26.3"),
+    key_setting!("key.attack", "key_key.attack", "1.0", "26.3"),
+    key_setting!("key.pick_item", "key_key.pickItem", "1.0", "26.3"),
+    key_setting!("key.chat", "key_key.chat", "1.0", "26.3"),
+    key_setting!("key.player_list", "key_key.playerlist", "1.0", "26.3"),
+    key_setting!("key.command", "key_key.command", "1.3.1", "26.3"),
+    key_setting!("key.screenshot", "key_key.screenshot", "1.7.2", "26.3"),
+    key_setting!(
+        "key.perspective",
+        "key_key.togglePerspective",
+        "1.7.2",
+        "26.3"
+    ),
+    key_setting!("key.fullscreen", "key_key.fullscreen", "1.7.3", "26.3"),
+    key_setting!("key.advancements", "key_key.advancements", "1.12", "26.3"),
+    key_setting!("key.smooth_camera", "key_key.smoothCamera", "1.7.2", "26.3"),
+    key_setting!(
+        "key.spectator_outlines",
+        "key_key.spectatorOutlines",
+        "1.8",
+        "26.3"
+    ),
+    key_setting!(
+        "key.save_toolbar",
+        "key_key.saveToolbarActivator",
+        "1.12",
+        "26.3"
+    ),
+    key_setting!(
+        "key.load_toolbar",
+        "key_key.loadToolbarActivator",
+        "1.12",
+        "26.3"
+    ),
+    key_setting!(
+        "key.social_interactions",
+        "key_key.socialInteractions",
+        "1.16.4",
+        "26.3"
+    ),
+    key_setting!(
+        "key.quick_actions",
+        "key_key.quickActions",
+        "1.21.6",
+        "26.3"
+    ),
+    key_setting!(
+        "key.spectator_hotbar",
+        "key_key.spectatorHotbar",
+        "1.21.9",
+        "26.3"
+    ),
+    key_setting!("key.friends", "key_key.friends", "26.2", "26.3"),
+    key_setting!("key.toggle_gui", "key_key.toggleGui", "1.21.11", "26.3"),
+    key_setting!(
+        "key.toggle_spectator_shader",
+        "key_key.toggleSpectatorShaderEffects",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!("key.hotbar.1", "key_key.hotbar.1", "1.7.2", "26.3"),
+    key_setting!("key.hotbar.2", "key_key.hotbar.2", "1.7.2", "26.3"),
+    key_setting!("key.hotbar.3", "key_key.hotbar.3", "1.7.2", "26.3"),
+    key_setting!("key.hotbar.4", "key_key.hotbar.4", "1.7.2", "26.3"),
+    key_setting!("key.hotbar.5", "key_key.hotbar.5", "1.7.2", "26.3"),
+    key_setting!("key.hotbar.6", "key_key.hotbar.6", "1.7.2", "26.3"),
+    key_setting!("key.hotbar.7", "key_key.hotbar.7", "1.7.2", "26.3"),
+    key_setting!("key.hotbar.8", "key_key.hotbar.8", "1.7.2", "26.3"),
+    key_setting!("key.hotbar.9", "key_key.hotbar.9", "1.7.2", "26.3"),
+    key_setting!(
+        "key.debug.overlay",
+        "key_key.debug.overlay",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.modifier",
+        "key_key.debug.modifier",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.reload_chunks",
+        "key_key.debug.reloadChunk",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.hitboxes",
+        "key_key.debug.showHitboxes",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.clear_chat",
+        "key_key.debug.clearChat",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!("key.debug.crash", "key_key.debug.crash", "1.21.11", "26.3"),
+    key_setting!(
+        "key.debug.chunk_borders",
+        "key_key.debug.showChunkBorders",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.advanced_tooltips",
+        "key_key.debug.showAdvancedTooltips",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.copy_recreate_command",
+        "key_key.debug.copyRecreateCommand",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.spectate",
+        "key_key.debug.spectate",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.switch_game_mode",
+        "key_key.debug.switchGameMode",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.options",
+        "key_key.debug.debugOptions",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.focus_pause",
+        "key_key.debug.focusPause",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.dump_dynamic_textures",
+        "key_key.debug.dumpDynamicTextures",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.reload_resource_packs",
+        "key_key.debug.reloadResourcePacks",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.profiling",
+        "key_key.debug.profiling",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.copy_location",
+        "key_key.debug.copyLocation",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.dump_version",
+        "key_key.debug.dumpVersion",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.profiling_chart",
+        "key_key.debug.profilingChart",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.fps_charts",
+        "key_key.debug.fpsCharts",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.network_charts",
+        "key_key.debug.networkCharts",
+        "1.21.11",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.lightmap_texture",
+        "key_key.debug.lightmapTexture",
+        "26.1",
+        "26.3"
+    ),
+    key_setting!(
+        "key.debug.improved_transparency",
+        "key_key.debug.improvedTransparency",
+        "26.3",
+        "26.3"
+    ),
+];
@@ -0,0 +1,127 @@
+use phf::phf_map;
+
+/// https://minecraft.wiki/w/Module:Protocol_version/Versions
+/// Covers 1.10-pre1, which introduced the options version field, through
+/// 18w47a, the last snapshot without embedded `version.json` metadata.
+pub(in crate::api::instance) const LEGACY_DATA_VERSIONS: phf::Map<&str, u32> = phf_map! {
+    "18w47a" => 1912,
+    "18w46a" => 1910,
+    "18w45a" => 1908,
+    "18w44a" => 1907,
+    "18w43c" => 1903,
+    "18w43b" => 1902,
+    "18w43a" => 1901,
+    "1.13.2" => 1631,
+    "1.13.2-pre2" => 1630,
+    "1.13.2-pre1" => 1629,
+    "1.13.1" => 1628,
+    "1.13.1-pre2" => 1627,
+    "1.13.1-pre1" => 1626,
+    "18w33a" => 1625,
+    "18w32a" => 1623,
+    "18w31a" => 1622,
+    "18w30b" => 1621,
+    "18w30a" => 1620,
+    "1.13" => 1519,
+    "1.13-pre10" => 1518,
+    "1.13-pre9" => 1517,
+    "1.13-pre8" => 1516,
+    "1.13-pre7" => 1513,
+    "1.13-pre6" => 1512,
+    "1.13-pre5" => 1511,
+    "1.13-pre4" => 1504,
+    "1.13-pre3" => 1503,
+    "1.13-pre2" => 1502,
+    "1.13-pre1" => 1501,
+    "18w22c" => 1499,
+    "18w22b" => 1498,
+    "18w22a" => 1497,
+    "18w21b" => 1496,
+    "18w21a" => 1495,
+    "18w20c" => 1493,
+    "18w20b" => 1491,
+    "18w20a" => 1489,
+    "18w19b" => 1485,
+    "18w19a" => 1484,
+    "18w16a" => 1483,
+    "18w15a" => 1482,
+    "18w14b" => 1481,
+    "18w14a" => 1479,
+    "18w11a" => 1478,
+    "18w10d" => 1477,
+    "18w10c" => 1476,
+    "18w10b" => 1474,
+    "18w10a" => 1473,
+    "18w09a" => 1472,
+    "18w08b" => 1471,
+    "18w08a" => 1470,
+    "18w07c" => 1469,
+    "18w07b" => 1468,
+    "18w07a" => 1467,
+    "18w06a" => 1466,
+    "18w05a" => 1464,
+    "18w03b" => 1463,
+    "18w03a" => 1462,
+    "18w02a" => 1461,
+    "18w01a" => 1459,
+    "17w50a" => 1457,
+    "17w49b" => 1455,
+    "17w49a" => 1454,
+    "17w48a" => 1453,
+    "17w47b" => 1452,
+    "17w47a" => 1451,
+    "17w46a" => 1449,
+    "17w45b" => 1448,
+    "17w45a" => 1447,
+    "17w43b" => 1445,
+    "17w43a" => 1444,
+    "1.12.2" => 1343,
+    "1.12.2-pre2" => 1342,
+    "1.12.2-pre1" => 1341,
+    "1.12.1" => 1241,
+    "1.12.1-pre1" => 1240,
+    "17w31a" => 1239,
+    "1.12" => 1139,
+    "1.12-pre7" => 1138,
+    "1.12-pre6" => 1137,
+    "1.12-pre5" => 1136,
+    "1.12-pre4" => 1135,
+    "1.12-pre3" => 1134,
+    "1.12-pre2" => 1133,
+    "1.12-pre1" => 1132,
+    "17w18b" => 1131,
+    "17w18a" => 1130,
+    "17w17b" => 1129,
+    "17w17a" => 1128,
+    "17w16b" => 1127,
+    "17w16a" => 1126,
+    "17w15a" => 1125,
+    "17w14a" => 1124,
+    "17w13b" => 1123,
+    "17w13a" => 1122,
+    "17w06a" => 1022,
+    "1.11.2" => 922,
+    "1.11.1" => 921,
+    "16w50a" => 920,
+    "1.11" => 819,
+    "1.11-pre1" => 818,
+    "16w44a" => 817,
+    "16w43a" => 816,
+    "16w42a" => 815,
+    "16w41a" => 814,
+    "16w40a" => 813,
+    "16w39c" => 812,
+    "16w39b" => 811,
+    "16w39a" => 809,
+    "16w38a" => 807,
+    "16w36a" => 805,
+    "16w35a" => 803,
+    "16w33a" => 802,
+    "16w32b" => 801,
+    "16w32a" => 800,
+    "1.10.2" => 512,
+    "1.10.1" => 511,
+    "1.10" => 510,
+    "1.10-pre2" => 507,
+    "1.10-pre1" => 506,
+};
@@ -0,0 +1,255 @@
+// Never treat these Minecraft keys as settings added by mods. NEVER_SYNC_KEYS are
+// not safe or useful to share; KNOWN_VANILLA_KEYS covers the vanilla catalog,
+// including entries that have a dedicated editor.
+pub(super) const NEVER_SYNC_KEYS: &[&str] = &[
+    "version",
+    "resourcePacks",
+    "incompatibleResourcePacks",
+    "lastServer",
+    "startedCleanly",
+    "tutorialStep",
+    "joinedFirstServer",
+    "onboardAccessibility",
+    "soundDevice",
+    "fullscreenResolution",
+    "overrideWidth",
+    "overrideHeight",
+    "difficulty",
+    "fboEnable",
+    "saturation",
+    "streamBytesPerPixel",
+    "streamMicVolume",
+    "streamGameVolume",
+    "streamKbps",
+    "streamFps",
+    "streamCompression",
+    "streamSendMetadata",
+    "streamPreferredServer",
+    "streamChatEnabled",
+    "streamChatUserFilter",
+    "streamMicToggleBehavior",
+    "skin",
+    "key_key.streamCommercial",
+    "key_key.streamPauseUnpause",
+    "key_key.streamStartStop",
+    "key_key.streamToggleMic",
+    "streamSystemVolume",
+    "showInventoryAchievementHint",
+    "enableWeakAttacks",
+    "skipRealms32bitWarning",
+    "key_Build",
+    "key_Load location",
+    "key_Save location",
+    "showFrameRate",
+    "limitFramerate",
+    "key_key.fog",
+    "chunksPerFrame",
+    "uploadsPerFrame",
+    "onlyShowSignedChat",
+    "skipFriendsListPromo",
+    "postProcessEnable",
+    "soundCategory_animals",
+    "soundCategory_blocks",
+    "soundCategory_mobs",
+    "soundCategory_players",
+    "soundCategory_records",
+    "shieldAnimation",
+];
+
+pub(super) const KNOWN_VANILLA_KEYS: &[&str] = &[
+    "version",
+    "ao",
+    "biomeBlendRadius",
+    "chunkSectionFadeInTime",
+    "cutoutLeaves",
+    "enableVsync",
+    "entityDistanceScaling",
+    "entityShadows",
+    "forceUnicodeFont",
+    "japaneseGlyphVariants",
+    "fov",
+    "fovEffectScale",
+    "darknessEffectScale",
+    "glintSpeed",
+    "glintStrength",
+    "preferredGraphicsBackend",
+    "graphicsPreset",
+    "prioritizeChunkUpdates",
+    "fullscreen",
+    "exclusiveFullscreen",
+    "macFullscreenMenuVisibility",
+    "gamma",
+    "guiScale",
+    "debugGuiScale",
+    "maxAnisotropyBit",
+    "textureFiltering",
+    "maxFps",
+    "improvedTransparency",
+    "inactivityFpsLimit",
+    "mipmapLevels",
+    "narrator",
+    "particles",
+    "reducedDebugInfo",
+    "renderClouds",
+    "cloudRange",
+    "renderDistance",
+    "simulationDistance",
+    "screenEffectScale",
+    "soundDevice",
+    "vignette",
+    "weatherRadius",
+    "autoJump",
+    "rotateWithMinecart",
+    "operatorItemsTab",
+    "autoSuggestions",
+    "chatColors",
+    "chatLinks",
+    "chatLinksPrompt",
+    "discrete_mouse_scroll",
+    "invertXMouse",
+    "invertYMouse",
+    "realmsNotifications",
+    "showSubtitles",
+    "directionalAudio",
+    "bobView",
+    "toggleCrouch",
+    "toggleSprint",
+    "toggleAttack",
+    "toggleUse",
+    "sprintWindow",
+    "darkMojangStudiosBackground",
+    "hideLightningFlashes",
+    "hideSplashTexts",
+    "mouseSensitivity",
+    "damageTiltStrength",
+    "highContrast",
+    "highContrastBlockOutline",
+    "narratorHotkey",
+    "resourcePacks",
+    "incompatibleResourcePacks",
+    "lastServer",
+    "lang",
+    "chatVisibility",
+    "chatOpacity",
+    "chatLineSpacing",
+    "textBackgroundOpacity",
+    "backgroundForChatOnly",
+    "hideServerAddress",
+    "advancedItemTooltips",
+    "pauseOnLostFocus",
+    "overrideWidth",
+    "overrideHeight",
+    "chatHeightFocused",
+    "chatDelay",
+    "chatHeightUnfocused",
+    "chatScale",
+    "chatWidth",
+    "notificationDisplayTime",
+    "useNativeTransport",
+    "mainHand",
+    "attackIndicator",
+    "tutorialStep",
+    "mouseWheelSensitivity",
+    "allowCursorChanges",
+    "quitShortcuts",
+    "ctrlClickEmulatesRightClick",
+    "glDebugVerbosity",
+    "skipMultiplayerWarning",
+    "hideMatchedNames",
+    "joinedFirstServer",
+    "syncChunkWrites",
+    "showAutosaveIndicator",
+    "allowServerListing",
+    "inGameNotification",
+    "sharePresence",
+    "onlyShowSecureChat",
+    "saveChatDrafts",
+    "panoramaScrollSpeed",
+    "telemetryOptInExtra",
+    "onboardAccessibility",
+    "menuBackgroundBlurriness",
+    "startedCleanly",
+    "musicToast",
+    "musicFrequency",
+    "key_key.attack",
+    "key_key.use",
+    "key_key.forward",
+    "key_key.left",
+    "key_key.back",
+    "key_key.right",
+    "key_key.jump",
+    "key_key.sneak",
+    "key_key.sprint",
+    "key_key.drop",
+    "key_key.inventory",
+    "key_key.chat",
+    "key_key.playerlist",
+    "key_key.pickItem",
+    "key_key.command",
+    "key_key.friends",
+    "key_key.socialInteractions",
+    "key_key.toggleGui",
+    "key_key.toggleSpectatorShaderEffects",
+    "key_key.screenshot",
+    "key_key.togglePerspective",
+    "key_key.smoothCamera",
+    "key_key.fullscreen",
+    "key_key.spectatorOutlines",
+    "key_key.spectatorHotbar",
+    "key_key.swapOffhand",
+    "key_key.saveToolbarActivator",
+    "key_key.loadToolbarActivator",
+    "key_key.advancements",
+    "key_key.quickActions",
+    "key_key.debug.overlay",
+    "key_key.debug.modifier",
+    "key_key.hotbar.1",
+    "key_key.hotbar.2",
+    "key_key.hotbar.3",
+    "key_key.hotbar.4",
+    "key_key.hotbar.5",
+    "key_key.hotbar.6",
+    "key_key.hotbar.7",
+    "key_key.hotbar.8",
+    "key_key.hotbar.9",
+    "key_key.debug.reloadChunk",
+    "key_key.debug.showHitboxes",
+    "key_key.debug.clearChat",
+    "key_key.debug.crash",
+    "key_key.debug.showChunkBorders",
+    "key_key.debug.showAdvancedTooltips",
+    "key_key.debug.copyRecreateCommand",
+    "key_key.debug.spectate",
+    "key_key.debug.switchGameMode",
+    "key_key.debug.debugOptions",
+    "key_key.debug.focusPause",
+    "key_key.debug.dumpDynamicTextures",
+    "key_key.debug.reloadResourcePacks",
+    "key_key.debug.profiling",
+    "key_key.debug.copyLocation",
+    "key_key.debug.dumpVersion",
+    "key_key.debug.profilingChart",
+    "key_key.debug.fpsCharts",
+    "key_key.debug.networkCharts",
+    "key_key.debug.lightmapTexture",
+    "key_key.debug.improvedTransparency",
+    "soundCategory_master",
+    "soundCategory_music",
+    "soundCategory_record",
+    "soundCategory_weather",
+    "soundCategory_block",
+    "soundCategory_hostile",
+    "soundCategory_neutral",
+    "soundCategory_player",
+    "soundCategory_ambient",
+    "soundCategory_voice",
+    "soundCategory_ui",
+    "modelPart_cape",
+    "modelPart_jacket",
+    "modelPart_left_sleeve",
+    "modelPart_right_sleeve",
+    "modelPart_left_pants_leg",
+    "modelPart_right_pants_leg",
+    "modelPart_hat",
+    "fullscreenResolution",
+];
@@ -0,0 +1,112 @@
+// Before Minecraft 1.13, options.txt stored key bindings as numbers. This table
+// converts those numbers to the key names used by current versions.
+pub(in crate::api::instance) const LEGACY_KEY_BINDINGS: &[(i32, &str)] = &[
+    (0, "key.keyboard.unknown"),
+    (1, "key.keyboard.escape"),
+    (2, "key.keyboard.1"),
+    (3, "key.keyboard.2"),
+    (4, "key.keyboard.3"),
+    (5, "key.keyboard.4"),
+    (6, "key.keyboard.5"),
+    (7, "key.keyboard.6"),
+    (8, "key.keyboard.7"),
+    (9, "key.keyboard.8"),
+    (10, "key.keyboard.9"),
+    (11, "key.keyboard.0"),
+    (12, "key.keyboard.minus"),
+    (13, "key.keyboard.equal"),
+    (14, "key.keyboard.backspace"),
+    (15, "key.keyboard.tab"),
+    (16, "key.keyboard.q"),
+    (17, "key.keyboard.w"),
+    (18, "key.keyboard.e"),
+    (19, "key.keyboard.r"),
+    (20, "key.keyboard.t"),
+    (21, "key.keyboard.y"),
+    (22, "key.keyboard.u"),
+    (23, "key.keyboard.i"),
+    (24, "key.keyboard.o"),
+    (25, "key.keyboard.p"),
+    (26, "key.keyboard.left.bracket"),
+    (27, "key.keyboard.right.bracket"),
+    (28, "key.keyboard.enter"),
+    (29, "key.keyboard.left.control"),
+    (30, "key.keyboard.a"),
+    (31, "key.keyboard.s"),
+    (32, "key.keyboard.d"),
+    (33, "key.keyboard.f"),
+    (34, "key.keyboard.g"),
+    (35, "key.keyboard.h"),
+    (36, "key.keyboard.j"),
+    (37, "key.keyboard.k"),
+    (38, "key.keyboard.l"),
+    (39, "key.keyboard.semicolon"),
+    (40, "key.keyboard.apostrophe"),
+    (41, "key.keyboard.grave.accent"),
+    (42, "key.keyboard.left.shift"),
+    (43, "key.keyboard.backslash"),
+    (44, "key.keyboard.z"),
+    (45, "key.keyboard.x"),
+    (46, "key.keyboard.c"),
+    (47, "key.keyboard.v"),
+    (48, "key.keyboard.b"),
+    (49, "key.keyboard.n"),
+    (50, "key.keyboard.m"),
+    (51, "key.keyboard.comma"),
+    (52, "key.keyboard.period"),
+    (53, "key.keyboard.slash"),
+    (54, "key.keyboard.right.shift"),
+    (55, "key.keyboard.keypad.multiply"),
+    (56, "key.keyboard.left.alt"),
+    (57, "key.keyboard.space"),
+    (58, "key.keyboard.caps.lock"),
+    (59, "key.keyboard.f1"),
+    (60, "key.keyboard.f2"),
+    (61, "key.keyboard.f3"),
+    (62, "key.keyboard.f4"),
+    (63, "key.keyboard.f5"),
+    (64, "key.keyboard.f6"),
+    (65, "key.keyboard.f7"),
+    (66, "key.keyboard.f8"),
+    (67, "key.keyboard.f9"),
+    (68, "key.keyboard.f10"),
+    (69, "key.keyboard.num.lock"),
+    (70, "key.keyboard.scroll.lock"),
+    (71, "key.keyboard.keypad.7"),
+    (72, "key.keyboard.keypad.8"),
+    (73, "key.keyboard.keypad.9"),
+    (74, "key.keyboard.keypad.subtract"),
+    (75, "key.keyboard.keypad.4"),
+    (76, "key.keyboard.keypad.5"),
+    (77, "key.keyboard.keypad.6"),
+    (78, "key.keyboard.keypad.add"),
+    (79, "key.keyboard.keypad.1"),
+    (80, "key.keyboard.keypad.2"),
+    (81, "key.keyboard.keypad.3"),
+    (82, "key.keyboard.keypad.0"),
+    (83, "key.keyboard.keypad.decimal"),
+    (87, "key.keyboard.f11"),
+    (88, "key.keyboard.f12"),
+    (100, "key.keyboard.f13"),
+    (101, "key.keyboard.f14"),
+    (102, "key.keyboard.f15"),
+    (141, "key.keyboard.keypad.equal"),
+    (156, "key.keyboard.keypad.enter"),
+    (157, "key.keyboard.right.control"),
+    (181, "key.keyboard.keypad.divide"),
+    (183, "key.keyboard.print.screen"),
+    (184, "key.keyboard.right.alt"),
+    (197, "key.keyboard.pause"),
+    (199, "key.keyboard.home"),
+    (200, "key.keyboard.up"),
+    (201, "key.keyboard.page.up"),
+    (203, "key.keyboard.left"),
+    (205, "key.keyboard.right"),
+    (207, "key.keyboard.end"),
+    (208, "key.keyboard.down"),
+    (209, "key.keyboard.page.down"),
+    (210, "key.keyboard.insert"),
+    (211, "key.keyboard.delete"),
+    (219, "key.keyboard.left.win"),
+    (220, "key.keyboard.right.win"),
+];
@@ -0,0 +1,452 @@
+//! Defines the Minecraft settings Modrinth knows how to read and write.
+//!
+//! File keys and version conversions live here. The frontend supplies the labels
+//! and translations shown to the user.
+
+mod accessibility;
+mod chat;
+mod controls;
+mod data_versions;
+mod known_vanilla_keys;
+mod legacy_key_bindings;
+mod sound;
+mod version_changes;
+mod video;
+
+use super::api_types::{
+    GameOptionEditorChoice, GameOptionEditorDefinition, GameOptionMappingKind,
+};
+
+pub(super) use data_versions::LEGACY_DATA_VERSIONS;
+use known_vanilla_keys::{KNOWN_VANILLA_KEYS, NEVER_SYNC_KEYS};
+pub(in crate::api::instance) use legacy_key_bindings::LEGACY_KEY_BINDINGS;
+pub(in crate::api::instance) use version_changes::*;
+
+#[derive(Clone, Copy)]
+pub(super) enum SettingEditor {
+    Boolean,
+    UnboundedInteger,
+    Integer {
+        min: i64,
+        max: i64,
+        step: i64,
+    },
+    UnboundedDecimal,
+    Decimal {
+        min: f64,
+        max: f64,
+        step: f64,
+        unit: Option<&'static str>,
+    },
+    Enum(&'static [&'static str]),
+    Language,
+    KeyBinding,
+}
+
+#[derive(Clone, Copy, Eq, PartialEq)]
+pub(super) enum ValueEncoding {
+    Bool,
+    Integer,
+    Decimal,
+    Enum(&'static [&'static str]),
+    QuotedEnum(&'static [&'static str]),
+    Text,
+    Graphics,
+    AmbientOcclusion,
+    ChatPreview,
+    Clouds,
+    GuiScale,
+    MenuBackgroundBlur,
+    MusicToast,
+    Fov,
+    KeyBinding,
+}
+
+pub(super) struct SupportedSetting {
+    pub(super) id: &'static str,
+    pub(super) keys: &'static [&'static str],
+    pub(super) versioned_keys: &'static [VersionedKey],
+    /// The README's observed range: versions whose fresh options file contains
+    /// this key. Versioned settings carry the same ranges on each physical key.
+    pub(super) since: &'static str,
+    pub(super) until: &'static str,
+    pub(super) category: &'static str,
+    pub(super) default_on: bool,
+    pub(super) editor: SettingEditor,
+    pub(super) encoding: ValueEncoding,
+}
+
+#[derive(Clone, Copy)]
+pub(super) struct VersionedKey {
+    pub(super) key: &'static str,
+    pub(super) since: &'static str,
+    pub(super) until: &'static str,
+    pub(super) mapping: GameOptionMappingKind,
+}
+
+pub(super) const BOOL: SettingEditor = SettingEditor::Boolean;
+pub(super) const UNIT_INTERVAL: SettingEditor = SettingEditor::Decimal {
+    min: 0.0,
+    max: 1.0,
+    step: 0.01,
+    unit: Some("percent"),
+};
+
+pub(super) const fn setting(
+    id: &'static str,
+    keys: &'static [&'static str],
+    category: &'static str,
+    default_on: bool,
+    editor: SettingEditor,
+    encoding: ValueEncoding,
+) -> SupportedSetting {
+    SupportedSetting {
+        id,
+        keys,
+        versioned_keys: &[],
+        since: "1.0",
+        until: "26.3",
+        category,
+        default_on,
+        editor,
+        encoding,
+    }
+}
+
+pub(super) const fn ranged_setting(
+    id: &'static str,
+    keys: &'static [&'static str],
+    since: &'static str,
+    until: &'static str,
+    category: &'static str,
+    default_on: bool,
+    editor: SettingEditor,
+    encoding: ValueEncoding,
+) -> SupportedSetting {
+    SupportedSetting {
+        id,
+        keys,
+        versioned_keys: &[],
+        since,
+        until,
+        category,
+        default_on,
+        editor,
+        encoding,
+    }
+}
+
+pub(super) const fn versioned_setting(
+    id: &'static str,
+    keys: &'static [&'static str],
+    versioned_keys: &'static [VersionedKey],
+    category: &'static str,
+    default_on: bool,
+    editor: SettingEditor,
+    encoding: ValueEncoding,
+) -> SupportedSetting {
+    SupportedSetting {
+        id,
+        keys,
+        versioned_keys,
+        since: "1.0",
+        until: "26.3",
+        category,
+        default_on,
+        editor,
+        encoding,
+    }
+}
+
+const SETTING_GROUPS: &[&[SupportedSetting]] = &[
+    video::SETTINGS,
+    sound::SETTINGS,
+    controls::SETTINGS,
+    chat::SETTINGS,
+    accessibility::SETTINGS,
+    GENERAL_SETTINGS,
+];
+
+const MAIN_HAND: &[&str] = &["left", "right"];
+const SHARE_PRESENCE: &[&str] = &["all", "limited", "none"];
+
+// These settings all use the common value formats above, so they can stay together.
+const GENERAL_SETTINGS: &[SupportedSetting] = &[
+    ranged_setting(
+        "main_hand",
+        &["mainHand"],
+        "1.9",
+        "26.3",
+        "skin_customization",
+        true,
+        SettingEditor::Enum(MAIN_HAND),
+        ValueEncoding::Enum(MAIN_HAND),
+    ),
+    versioned_setting(
+        "cape",
+        &["modelPart_cape", "showCape"],
+        version_changes::CAPE_KEYS,
+        "skin_customization",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "hat",
+        &["modelPart_hat"],
+        "1.8",
+        "26.3",
+        "skin_customization",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "jacket",
+        &["modelPart_jacket"],
+        "1.8",
+        "26.3",
+        "skin_customization",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "left_sleeve",
+        &["modelPart_left_sleeve"],
+        "1.8",
+        "26.3",
+        "skin_customization",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "right_sleeve",
+        &["modelPart_right_sleeve"],
+        "1.8",
+        "26.3",
+        "skin_customization",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "left_pants_leg",
+        &["modelPart_left_pants_leg"],
+        "1.8",
+        "26.3",
+        "skin_customization",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "right_pants_leg",
+        &["modelPart_right_pants_leg"],
+        "1.8",
+        "26.3",
+        "skin_customization",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "allow_server_listing",
+        &["allowServerListing"],
+        "1.18",
+        "26.3",
+        "online",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "realms_notifications",
+        &["realmsNotifications"],
+        "1.8.9",
+        "26.3",
+        "online",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "hide_server_address",
+        &["hideServerAddress"],
+        "1.3.2",
+        "26.3",
+        "online",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "server_textures",
+        &["serverTextures"],
+        "1.3.1",
+        "1.7.5",
+        "online",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "snooper",
+        &["snooperEnabled"],
+        "1.3.1",
+        "1.17.1",
+        "online",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "extra_telemetry",
+        &["telemetryOptInExtra"],
+        "1.19.3",
+        "26.3",
+        "online",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "in_game_notifications",
+        &["inGameNotification"],
+        "26.2",
+        "26.3",
+        "online",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "share_presence",
+        &["sharePresence"],
+        "26.2",
+        "26.3",
+        "online",
+        true,
+        SettingEditor::Enum(SHARE_PRESENCE),
+        ValueEncoding::QuotedEnum(SHARE_PRESENCE),
+    ),
+];
+
+pub(super) fn all_supported_settings()
+-> impl Iterator<Item = &'static SupportedSetting> {
+    SETTING_GROUPS.iter().flat_map(|group| group.iter())
+}
+
+pub(super) fn setting_by_id(
+    option_id: &str,
+) -> Option<&'static SupportedSetting> {
+    all_supported_settings().find(|setting| setting.id == option_id)
+}
+
+pub(super) fn setting_by_file_key(
+    key: &str,
+) -> Option<&'static SupportedSetting> {
+    all_supported_settings().find(|setting| setting.keys.contains(&key))
+}
+
+pub(super) fn setting_available_for_version(
+    setting: &SupportedSetting,
+    version: &str,
+) -> bool {
+    if !setting.versioned_keys.is_empty() {
+        return physical_variant_for_version(setting, version).is_some();
+    }
+    let Some(version) = release_version(version) else {
+        return false;
+    };
+    release_version(setting.since).is_some_and(|since| since <= version)
+        && release_version(setting.until).is_some_and(|until| version <= until)
+}
+
+pub(super) fn target_key_for_version<'a>(
+    setting: &'a SupportedSetting,
+    version: &str,
+) -> Option<&'a str> {
+    if setting.versioned_keys.is_empty() {
+        setting_available_for_version(setting, version)
+            .then(|| setting.keys.first().copied())
+            .flatten()
+    } else {
+        physical_variant_for_version(setting, version)
+            .map(|variant| variant.key)
+    }
+}
+
+pub(super) fn is_never_sync_key(key: &str) -> bool {
+    NEVER_SYNC_KEYS.contains(&key)
+        || KNOWN_VANILLA_KEYS.contains(&key)
+        || key.starts_with("skip")
+        || key.starts_with("hideBundleTutorial")
+        || key.starts_with("key_") && !key.starts_with("key_key.")
+}
+
+pub(super) fn editor_for(
+    setting: &SupportedSetting,
+) -> GameOptionEditorDefinition {
+    let mut editor = GameOptionEditorDefinition {
+        type_: String::new(),
+        min: None,
+        max: None,
+        step: None,
+        unit: None,
+        choices: Vec::new(),
+    };
+    match setting.editor {
+        SettingEditor::Boolean => editor.type_ = "bool".to_string(),
+        SettingEditor::UnboundedInteger => {
+            editor.type_ = "integer".to_string();
+            editor.step = Some(1.0);
+        }
+        SettingEditor::Integer { min, max, step } => {
+            editor.type_ = "integer".to_string();
+            editor.min = Some(min as f64);
+            editor.max = Some(max as f64);
+            editor.step = Some(step as f64);
+        }
+        SettingEditor::UnboundedDecimal => {
+            editor.type_ = "decimal".to_string();
+            editor.step = Some(0.01);
+        }
+        SettingEditor::Decimal {
+            min,
+            max,
+            step,
+            unit,
+        } => {
+            editor.type_ = "decimal".to_string();
+            editor.min = Some(min);
+            editor.max = Some(max);
+            editor.step = Some(step);
+            editor.unit = unit.map(str::to_string);
+        }
+        SettingEditor::Enum(choices) => {
+            editor.type_ = "enum".to_string();
+            editor.choices = choices
+                .iter()
+                .map(|value| GameOptionEditorChoice {
+                    value: (*value).to_string(),
+                })
+                .collect();
+        }
+        SettingEditor::Language => editor.type_ = "text".to_string(),
+        SettingEditor::KeyBinding => editor.type_ = "key_binding".to_string(),
+    }
+    editor
+}
+
+pub(super) fn custom_setting_editor() -> GameOptionEditorDefinition {
+    GameOptionEditorDefinition {
+        type_: "external_raw".to_string(),
+        min: None,
+        max: None,
+        step: None,
+        unit: None,
+        choices: Vec::new(),
+    }
+}
@@ -0,0 +1,177 @@
+use super::{
+    BOOL, SettingEditor, SupportedSetting, UNIT_INTERVAL, ValueEncoding,
+    ranged_setting, version_changes, versioned_setting,
+};
+
+const MUSIC_TOAST: &[&str] = &["never", "pause", "pause_and_toast"];
+const MUSIC_FREQUENCY: &[&str] = &["CONSTANT", "DEFAULT", "FREQUENT"];
+
+pub(super) const SETTINGS: &[SupportedSetting] = &[
+    ranged_setting(
+        "language",
+        &["lang"],
+        "1.1",
+        "26.3",
+        "language",
+        true,
+        SettingEditor::Language,
+        ValueEncoding::Text,
+    ),
+    ranged_setting(
+        "force_unicode_font",
+        &["forceUnicodeFont"],
+        "1.7.2",
+        "26.3",
+        "language",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "japanese_glyph_variants",
+        &["japaneseGlyphVariants"],
+        "1.20.5",
+        "26.3",
+        "language",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "directional_audio",
+        &["directionalAudio"],
+        "1.19",
+        "26.3",
+        "music_and_sound",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    versioned_setting(
+        "music_toast",
+        &["musicToast", "showNowPlayingToast"],
+        version_changes::MUSIC_TOAST_KEYS,
+        "music_and_sound",
+        true,
+        SettingEditor::Enum(MUSIC_TOAST),
+        ValueEncoding::MusicToast,
+    ),
+    ranged_setting(
+        "music_frequency",
+        &["musicFrequency"],
+        "1.21.6",
+        "26.3",
+        "music_and_sound",
+        true,
+        SettingEditor::Enum(MUSIC_FREQUENCY),
+        ValueEncoding::QuotedEnum(MUSIC_FREQUENCY),
+    ),
+    versioned_setting(
+        "master_volume",
+        &["soundCategory_master", "sound"],
+        version_changes::MASTER_VOLUME_KEYS,
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    versioned_setting(
+        "music_volume",
+        &["soundCategory_music", "music"],
+        version_changes::MUSIC_VOLUME_KEYS,
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "record_volume",
+        &["soundCategory_record"],
+        "1.7.2",
+        "26.3",
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "weather_volume",
+        &["soundCategory_weather"],
+        "1.7.2",
+        "26.3",
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "blocks_volume",
+        &["soundCategory_block"],
+        "1.7.2",
+        "26.3",
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "hostile_volume",
+        &["soundCategory_hostile"],
+        "1.7.2",
+        "26.3",
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "neutral_volume",
+        &["soundCategory_neutral"],
+        "1.7.2",
+        "26.3",
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "players_volume",
+        &["soundCategory_player"],
+        "1.7.2",
+        "26.3",
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "ambient_volume",
+        &["soundCategory_ambient"],
+        "1.7.2",
+        "26.3",
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "voice_volume",
+        &["soundCategory_voice"],
+        "1.9",
+        "26.3",
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "ui_volume",
+        &["soundCategory_ui"],
+        "1.21.6",
+        "26.3",
+        "music_and_sound",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+];
@@ -0,0 +1,969 @@
+//! Handles settings Minecraft renamed or stored differently between versions.
+
+use super::super::api_types::canonical_values_equal;
+use super::super::options_file::{
+    GameOptionsDocument, input_error, validate_raw_key_value,
+};
+use super::{
+    GameOptionMappingKind, LEGACY_KEY_BINDINGS, SettingEditor,
+    SupportedSetting, ValueEncoding, VersionedKey,
+    setting_available_for_version,
+};
+use crate::state::{CanonicalValue, StoredOption};
+
+const GRAPHICS_VALUES: &[&str] = &["fast", "fancy", "fabulous", "custom"];
+const CLOUD_VALUES: &[&str] = &["false", "fast", "true"];
+const MUSIC_TOAST_VALUES: &[&str] = &["never", "pause", "pause_and_toast"];
+
+fn decode_string_token(raw: &str) -> Option<String> {
+    if raw.starts_with('"') {
+        serde_json::from_str(raw).ok()
+    } else {
+        Some(raw.to_string())
+    }
+}
+
+fn encode_string_token(value: &str) -> Option<String> {
+    serde_json::to_string(value).ok()
+}
+
+pub(in crate::api::instance) const GRAPHICS_KEYS: &[VersionedKey] = &[
+    VersionedKey {
+        key: "fancyGraphics",
+        since: "1.0",
+        until: "1.15.2",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "graphicsMode",
+        since: "1.16",
+        until: "1.21.10",
+        mapping: GameOptionMappingKind::Migrated,
+    },
+    VersionedKey {
+        key: "graphicsPreset",
+        since: "1.21.11",
+        until: "26.3",
+        mapping: GameOptionMappingKind::Direct,
+    },
+];
+
+pub(in crate::api::instance) const AMBIENT_OCCLUSION_KEYS: &[VersionedKey] = &[
+    VersionedKey {
+        key: "ao",
+        since: "1.0",
+        until: "1.4.7",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "ao",
+        since: "1.5.1",
+        until: "1.19.2",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "ao",
+        since: "1.19.3",
+        until: "26.3",
+        mapping: GameOptionMappingKind::Direct,
+    },
+];
+
+pub(in crate::api::instance) const FOV_KEYS: &[VersionedKey] =
+    &[VersionedKey {
+        key: "fov",
+        since: "1.0",
+        until: "26.3",
+        mapping: GameOptionMappingKind::Direct,
+    }];
+
+pub(in crate::api::instance) const CLOUD_KEYS: &[VersionedKey] = &[
+    VersionedKey {
+        key: "clouds",
+        since: "1.0",
+        until: "1.7.10",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "renderClouds",
+        since: "1.8",
+        until: "1.8",
+        mapping: GameOptionMappingKind::Migrated,
+    },
+    VersionedKey {
+        key: "renderClouds",
+        since: "1.8.1",
+        until: "26.3",
+        mapping: GameOptionMappingKind::Direct,
+    },
+];
+
+pub(in crate::api::instance) const CHAT_PREVIEW_KEYS: &[VersionedKey] = &[
+    VersionedKey {
+        key: "chatPreview",
+        since: "1.19",
+        until: "1.19",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "chatPreview",
+        since: "1.19.1",
+        until: "1.19.2",
+        mapping: GameOptionMappingKind::Direct,
+    },
+];
+
+pub(in crate::api::instance) const MENU_BACKGROUND_BLUR_KEYS:
+    &[VersionedKey] = &[
+    VersionedKey {
+        key: "menuBackgroundBlurriness",
+        since: "1.20.5",
+        until: "1.20.6",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "menuBackgroundBlurriness",
+        since: "1.21",
+        until: "26.3",
+        mapping: GameOptionMappingKind::Direct,
+    },
+];
+
+pub(in crate::api::instance) const MASTER_VOLUME_KEYS: &[VersionedKey] = &[
+    VersionedKey {
+        key: "sound",
+        since: "1.0",
+        until: "1.6.4",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "soundCategory_master",
+        since: "1.7.2",
+        until: "26.3",
+        mapping: GameOptionMappingKind::Direct,
+    },
+];
+
+pub(in crate::api::instance) const MUSIC_VOLUME_KEYS: &[VersionedKey] = &[
+    VersionedKey {
+        key: "music",
+        since: "1.0",
+        until: "1.6.4",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "soundCategory_music",
+        since: "1.7.2",
+        until: "26.3",
+        mapping: GameOptionMappingKind::Direct,
+    },
+];
+
+pub(in crate::api::instance) const CAPE_KEYS: &[VersionedKey] = &[
+    VersionedKey {
+        key: "showCape",
+        since: "1.4.2",
+        until: "1.7.10",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "modelPart_cape",
+        since: "1.8",
+        until: "26.3",
+        mapping: GameOptionMappingKind::Direct,
+    },
+];
+
+pub(in crate::api::instance) const MUSIC_TOAST_KEYS: &[VersionedKey] = &[
+    VersionedKey {
+        key: "showNowPlayingToast",
+        since: "1.21.6",
+        until: "1.21.10",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "musicToast",
+        since: "1.21.11",
+        until: "26.3",
+        mapping: GameOptionMappingKind::Direct,
+    },
+];
+
+pub(in crate::api::instance) const SWAP_OFFHAND_KEYS: &[VersionedKey] = &[
+    VersionedKey {
+        key: "key_key.swapHands",
+        since: "1.9",
+        until: "1.15.2",
+        mapping: GameOptionMappingKind::Legacy,
+    },
+    VersionedKey {
+        key: "key_key.swapOffhand",
+        since: "1.16",
+        until: "26.3",
+        mapping: GameOptionMappingKind::Direct,
+    },
+];
+
+pub(in crate::api::instance) fn release_version(
+    version: &str,
+) -> Option<(u32, u32, u32)> {
+    let components = version
+        .split('.')
+        .map(|component| component.parse::<u32>())
+        .collect::<Result<Vec<_>, _>>()
+        .ok()?;
+    match components.as_slice() {
+        [major, minor] => Some((*major, *minor, 0)),
+        [major, minor, patch] => Some((*major, *minor, *patch)),
+        _ => None,
+    }
+}
+
+pub(in crate::api::instance) fn physical_variant_for_version<'a>(
+    definition: &'a SupportedSetting,
+    version: &str,
+) -> Option<&'a VersionedKey> {
+    let version = release_version(version)?;
+    definition.versioned_keys.iter().find(|variant| {
+        let Some(since) = release_version(variant.since) else {
+            return false;
+        };
+        let Some(until) = release_version(variant.until) else {
+            return false;
+        };
+        version >= since && version <= until
+    })
+}
+
+pub(in crate::api::instance) fn physical_variant_for_present_key<'a>(
+    definition: &'a SupportedSetting,
+    key: &str,
+    version: &str,
+) -> Option<&'a VersionedKey> {
+    let version = release_version(version)?;
+    definition.versioned_keys.iter().rev().find(|variant| {
+        variant.key == key
+            && release_version(variant.since)
+                .is_some_and(|since| since <= version)
+            && release_version(variant.until)
+                .is_some_and(|until| version <= until)
+    })
+}
+
+pub(in crate::api::instance) fn uses_modern_key_tokens(version: &str) -> bool {
+    release_version(version).is_some_and(|version| version >= (1, 13, 0))
+}
+
+pub(in crate::api::instance) fn split_key_binding(
+    value: &str,
+) -> (&str, Option<&str>) {
+    value
+        .split_once(':')
+        .map_or((value, None), |(key, modifier)| (key, Some(modifier)))
+}
+
+pub(in crate::api::instance) fn append_key_modifier(
+    mut key: String,
+    modifier: Option<&str>,
+) -> String {
+    if let Some(modifier) = modifier {
+        key.push(':');
+        key.push_str(modifier);
+    }
+    key
+}
+
+pub(in crate::api::instance) fn legacy_key_binding_to_token(
+    value: &str,
+) -> Option<String> {
+    let (key, modifier) = split_key_binding(value);
+    let key = key.parse::<i32>().ok()?;
+    let token = match key {
+        -100 => "key.mouse.left".to_string(),
+        -99 => "key.mouse.right".to_string(),
+        -98 => "key.mouse.middle".to_string(),
+        -97..=-85 => format!("key.mouse.{}", key + 101),
+        _ => LEGACY_KEY_BINDINGS
+            .iter()
+            .find(|(legacy, _)| *legacy == key)
+            .map(|(_, token)| (*token).to_string())?,
+    };
+    Some(append_key_modifier(token, modifier))
+}
+
+pub(in crate::api::instance) fn token_key_binding_to_legacy(
+    value: &str,
+) -> Option<String> {
+    let (token, modifier) = split_key_binding(value);
+    let key = match token {
+        "key.mouse.left" => -100,
+        "key.mouse.right" => -99,
+        "key.mouse.middle" => -98,
+        _ => {
+            if let Some(button) = token.strip_prefix("key.mouse.") {
+                let button = button.parse::<i32>().ok()?;
+                if !(4..=16).contains(&button) {
+                    return None;
+                }
+                button - 101
+            } else {
+                LEGACY_KEY_BINDINGS
+                    .iter()
+                    .find(|(_, candidate)| *candidate == token)
+                    .map(|(legacy, _)| *legacy)?
+            }
+        }
+    };
+    Some(append_key_modifier(key.to_string(), modifier))
+}
+
+pub(in crate::api::instance) fn valid_modern_key_binding(value: &str) -> bool {
+    let (key, modifier) = split_key_binding(value);
+    let key_valid = ["key.keyboard.", "key.mouse.", "scancode."]
+        .into_iter()
+        .find_map(|prefix| key.strip_prefix(prefix))
+        .is_some_and(|identifier| {
+            !identifier.is_empty()
+                && identifier.chars().all(|character| {
+                    character.is_ascii_alphanumeric()
+                        || matches!(character, '.' | '_' | '-')
+                })
+        });
+    key_valid
+        && modifier.is_none_or(|modifier| {
+            !modifier.is_empty()
+                && modifier.len() <= 64
+                && modifier.chars().all(|character| {
+                    character.is_ascii_alphanumeric()
+                        || matches!(character, '.' | '_' | '-' | ':' | '+')
+                })
+        })
+}
+
+pub(in crate::api::instance) fn supported_settings_cover_game_version(
+    version: &str,
+) -> bool {
+    if version.contains('w') || version.contains("snapshot") {
+        return false;
+    }
+    let components = version
+        .split('.')
+        .map(|component| component.parse::<u32>())
+        .collect::<Result<Vec<_>, _>>();
+    let Ok(components) = components else {
+        return false;
+    };
+    match components.as_slice() {
+        [1, minor] => *minor <= 21,
+        [1, minor, patch] => *minor < 21 || (*minor == 21 && *patch <= 11),
+        [26, minor] | [26, minor, _] => (1..=3).contains(minor),
+        _ => false,
+    }
+}
+
+pub(in crate::api::instance) fn decode_value(
+    definition: &SupportedSetting,
+    physical_key: &str,
+    raw: &str,
+) -> Option<CanonicalValue> {
+    match definition.encoding {
+        ValueEncoding::Bool => match raw {
+            "true" => Some(CanonicalValue::Bool(true)),
+            "false" => Some(CanonicalValue::Bool(false)),
+            _ => None,
+        },
+        ValueEncoding::Integer => {
+            raw.parse::<i64>().ok().map(CanonicalValue::Integer)
+        }
+        ValueEncoding::Decimal => raw
+            .parse::<f64>()
+            .ok()
+            .filter(|value| value.is_finite())
+            .map(|_| CanonicalValue::Decimal(raw.to_string())),
+        ValueEncoding::Enum(choices) => {
+            let value = decode_string_token(raw)?;
+            choices
+                .contains(&value.as_str())
+                .then_some(CanonicalValue::Enum(value))
+        }
+        ValueEncoding::QuotedEnum(choices) => {
+            let value = decode_string_token(raw)?;
+            choices
+                .contains(&value.as_str())
+                .then_some(CanonicalValue::Enum(value))
+        }
+        ValueEncoding::Text => Some(CanonicalValue::Text(raw.to_string())),
+        ValueEncoding::KeyBinding => {
+            if valid_modern_key_binding(raw) {
+                Some(CanonicalValue::KeyBinding(raw.to_string()))
+            } else {
+                legacy_key_binding_to_token(raw).map(CanonicalValue::KeyBinding)
+            }
+        }
+        ValueEncoding::Fov => raw.parse::<f64>().ok().and_then(|value| {
+            if value.fract() == 0.0 && (30.0..=110.0).contains(&value) {
+                return Some(CanonicalValue::Integer(value as i64));
+            }
+            let degrees = value * 40.0 + 70.0;
+            (value.is_finite()
+                && (-1.0..=1.0).contains(&value)
+                && (degrees - degrees.round()).abs() <= 0.000_001)
+                .then(|| CanonicalValue::Integer(degrees.round() as i64))
+        }),
+        ValueEncoding::GuiScale => {
+            raw.parse::<i64>().ok().map(CanonicalValue::Integer)
+        }
+        ValueEncoding::MenuBackgroundBlur => raw
+            .parse::<f64>()
+            .ok()
+            .filter(|value| value.is_finite() && value.fract() == 0.0)
+            .map(|value| CanonicalValue::Integer(value as i64)),
+        ValueEncoding::Graphics => {
+            let raw = decode_string_token(raw)?;
+            let value = match physical_key {
+                "fancyGraphics" => match raw.as_str() {
+                    "false" => "fast",
+                    "true" => "fancy",
+                    _ => return None,
+                },
+                "graphicsMode" => match raw.as_str() {
+                    "0" => "fast",
+                    "1" => "fancy",
+                    "2" => "fabulous",
+                    _ => return None,
+                },
+                "graphicsPreset" if GRAPHICS_VALUES.contains(&raw.as_str()) => {
+                    raw.as_str()
+                }
+                _ => return None,
+            };
+            Some(CanonicalValue::Enum(value.to_string()))
+        }
+        ValueEncoding::AmbientOcclusion => {
+            let value = match raw {
+                "false" | "0" => "off",
+                "true" => "on",
+                "1" => "minimum",
+                "2" => "maximum",
+                _ => return None,
+            };
+            Some(CanonicalValue::Enum(value.to_string()))
+        }
+        ValueEncoding::ChatPreview => {
+            let value = match raw {
+                "false" | "0" => "0",
+                "1" => "1",
+                "true" | "2" => "2",
+                _ => return None,
+            };
+            Some(CanonicalValue::Enum(value.to_string()))
+        }
+        ValueEncoding::Clouds => {
+            let raw = decode_string_token(raw)?;
+            CLOUD_VALUES
+                .contains(&raw.as_str())
+                .then_some(CanonicalValue::Enum(raw))
+        }
+        ValueEncoding::MusicToast => {
+            let raw = decode_string_token(raw)?;
+            let value = match (physical_key, raw.as_str()) {
+                ("showNowPlayingToast", "false") => "never",
+                ("showNowPlayingToast", "true") => "pause_and_toast",
+                ("musicToast", "never" | "pause" | "pause_and_toast") => {
+                    raw.as_str()
+                }
+                _ => return None,
+            };
+            Some(CanonicalValue::Enum(value.to_string()))
+        }
+    }
+}
+
+pub(in crate::api::instance) fn encode_value(
+    definition: &SupportedSetting,
+    physical_key: &str,
+    value: &CanonicalValue,
+    game_version: &str,
+    current_raw: Option<&str>,
+) -> Option<String> {
+    if !setting_available_for_version(definition, game_version) {
+        return None;
+    }
+    if let Some(current_raw) = current_raw
+        && physical_representation_supported_for_target(
+            definition,
+            physical_key,
+            current_raw,
+            game_version,
+        )
+        && decode_value(definition, physical_key, current_raw)
+            .as_ref()
+            .is_some_and(|current| canonical_values_equal(current, value))
+    {
+        return Some(current_raw.to_string());
+    }
+    match (definition.encoding, value) {
+        (ValueEncoding::Bool, CanonicalValue::Bool(value)) => {
+            Some(value.to_string())
+        }
+        (ValueEncoding::Integer, CanonicalValue::Integer(value)) => {
+            Some(value.to_string())
+        }
+        (ValueEncoding::Decimal, CanonicalValue::Decimal(value)) => {
+            Some(value.clone())
+        }
+        (ValueEncoding::Decimal, CanonicalValue::Integer(value)) => {
+            Some(value.to_string())
+        }
+        (ValueEncoding::Enum(choices), CanonicalValue::Enum(value))
+            if choices.contains(&value.as_str()) =>
+        {
+            if current_raw.is_some_and(|raw| raw.starts_with('"')) {
+                encode_string_token(value)
+            } else {
+                Some(value.clone())
+            }
+        }
+        (ValueEncoding::QuotedEnum(choices), CanonicalValue::Enum(value))
+            if choices.contains(&value.as_str()) =>
+        {
+            encode_string_token(value)
+        }
+        (ValueEncoding::Text, CanonicalValue::Text(value)) => {
+            Some(value.clone())
+        }
+        (ValueEncoding::KeyBinding, CanonicalValue::KeyBinding(value))
+            if valid_modern_key_binding(value) =>
+        {
+            if !uses_modern_key_tokens(game_version) {
+                token_key_binding_to_legacy(value)
+            } else {
+                Some(value.clone())
+            }
+        }
+        (ValueEncoding::Fov, CanonicalValue::Integer(value))
+            if (30..=110).contains(value) =>
+        {
+            let normalized = (*value as f64 - 70.0) / 40.0;
+            Some(format_decimal(normalized))
+        }
+        (ValueEncoding::GuiScale, CanonicalValue::Integer(value))
+            if (0..=8).contains(value)
+                && (release_version(game_version)
+                    .is_some_and(|version| version >= (1, 13, 0))
+                    || *value <= 3) =>
+        {
+            Some(value.to_string())
+        }
+        (ValueEncoding::MenuBackgroundBlur, CanonicalValue::Integer(value))
+            if (0..=10).contains(value) =>
+        {
+            if release_version(game_version)
+                .is_some_and(|version| version >= (1, 21, 0))
+            {
+                Some(value.to_string())
+            } else {
+                Some(format!("{value}.0"))
+            }
+        }
+        (ValueEncoding::Graphics, CanonicalValue::Enum(value)) => {
+            match physical_key {
+                "fancyGraphics" => match value.as_str() {
+                    "fast" => Some("false".to_string()),
+                    "fancy" => Some("true".to_string()),
+                    _ => None,
+                },
+                "graphicsMode" => match value.as_str() {
+                    "fast" => Some("0".to_string()),
+                    "fancy" => Some("1".to_string()),
+                    "fabulous" => Some("2".to_string()),
+                    _ => None,
+                },
+                "graphicsPreset"
+                    if GRAPHICS_VALUES.contains(&value.as_str()) =>
+                {
+                    encode_string_token(value)
+                }
+                _ => None,
+            }
+        }
+        (ValueEncoding::AmbientOcclusion, CanonicalValue::Enum(value)) => {
+            let version = release_version(game_version)?;
+            if ((1, 5, 1)..=(1, 19, 2)).contains(&version) {
+                match value.as_str() {
+                    "off" => Some("0".to_string()),
+                    "minimum" => Some("1".to_string()),
+                    "maximum" => Some("2".to_string()),
+                    _ => None,
+                }
+            } else {
+                match value.as_str() {
+                    "off" => Some("false".to_string()),
+                    "on" => Some("true".to_string()),
+                    _ => None,
+                }
+            }
+        }
+        (ValueEncoding::ChatPreview, CanonicalValue::Enum(value)) => {
+            if release_version(game_version) == Some((1, 19, 0)) {
+                match value.as_str() {
+                    "0" => Some("false".to_string()),
+                    "2" => Some("true".to_string()),
+                    _ => None,
+                }
+            } else if matches!(value.as_str(), "0" | "1" | "2") {
+                Some(value.clone())
+            } else {
+                None
+            }
+        }
+        (ValueEncoding::Clouds, CanonicalValue::Enum(value)) => {
+            let version = release_version(game_version)?;
+            if version <= (1, 8, 0) {
+                match value.as_str() {
+                    "false" | "true" => Some(value.clone()),
+                    _ => None,
+                }
+            } else if CLOUD_VALUES.contains(&value.as_str()) {
+                Some(value.clone())
+            } else {
+                None
+            }
+        }
+        (ValueEncoding::MusicToast, CanonicalValue::Enum(value)) => {
+            match physical_key {
+                "showNowPlayingToast" => match value.as_str() {
+                    "never" => Some("false".to_string()),
+                    "pause_and_toast" => Some("true".to_string()),
+                    _ => None,
+                },
+                "musicToast"
+                    if MUSIC_TOAST_VALUES.contains(&value.as_str()) =>
+                {
+                    encode_string_token(value)
+                }
+                _ => None,
+            }
+        }
+        _ => None,
+    }
+}
+
+fn validate_value(
+    definition: Option<&SupportedSetting>,
+    value: &CanonicalValue,
+    enforce_editor_increment: bool,
+) -> crate::Result<()> {
+    if let Some(definition) = definition {
+        let type_valid = match definition.encoding {
+            ValueEncoding::Bool => matches!(value, CanonicalValue::Bool(_)),
+            ValueEncoding::Integer
+            | ValueEncoding::GuiScale
+            | ValueEncoding::MenuBackgroundBlur => {
+                matches!(value, CanonicalValue::Integer(_))
+            }
+            ValueEncoding::Decimal => matches!(
+                value,
+                CanonicalValue::Decimal(_) | CanonicalValue::Integer(_)
+            ),
+            ValueEncoding::Enum(_)
+            | ValueEncoding::QuotedEnum(_)
+            | ValueEncoding::Graphics
+            | ValueEncoding::AmbientOcclusion
+            | ValueEncoding::ChatPreview
+            | ValueEncoding::Clouds
+            | ValueEncoding::MusicToast => {
+                matches!(value, CanonicalValue::Enum(_))
+            }
+            ValueEncoding::Text => matches!(value, CanonicalValue::Text(_)),
+            ValueEncoding::Fov => matches!(value, CanonicalValue::Integer(_)),
+            ValueEncoding::KeyBinding => {
+                matches!(value, CanonicalValue::KeyBinding(_))
+            }
+        };
+        if !type_valid {
+            return Err(input_error(format!(
+                "Invalid value type for {}",
+                definition.id
+            )));
+        }
+        match (definition.editor, value) {
+            (
+                SettingEditor::UnboundedDecimal,
+                CanonicalValue::Decimal(value),
+            ) if value
+                .parse::<f64>()
+                .ok()
+                .is_none_or(|value| !value.is_finite()) =>
+            {
+                return Err(input_error("Invalid decimal value"));
+            }
+            (
+                SettingEditor::Integer { min, max, step },
+                CanonicalValue::Integer(value),
+            ) if *value < min
+                || *value > max
+                || enforce_editor_increment
+                    && step > 0
+                    && (*value - min) % step != 0 =>
+            {
+                return Err(input_error(format!(
+                    "{} is outside its supported range or increment",
+                    definition.id
+                )));
+            }
+            (
+                SettingEditor::Decimal { min, max, step, .. },
+                CanonicalValue::Decimal(value),
+            ) => {
+                let parsed = value
+                    .parse::<f64>()
+                    .map_err(|_| input_error("Invalid decimal value"))?;
+                let increment = (parsed - min) / step;
+                if !parsed.is_finite()
+                    || parsed < min
+                    || parsed > max
+                    || enforce_editor_increment
+                        && step > 0.0
+                        && (increment - increment.round()).abs() > 0.000_001
+                {
+                    return Err(input_error(format!(
+                        "{} is outside its supported range or increment",
+                        definition.id
+                    )));
+                }
+            }
+            (
+                SettingEditor::Decimal { min, max, step, .. },
+                CanonicalValue::Integer(value),
+            ) => {
+                let parsed = *value as f64;
+                let increment = (parsed - min) / step;
+                if parsed < min
+                    || parsed > max
+                    || enforce_editor_increment
+                        && step > 0.0
+                        && (increment - increment.round()).abs() > 0.000_001
+                {
+                    return Err(input_error(format!(
+                        "{} is outside its supported range or increment",
+                        definition.id
+                    )));
+                }
+            }
+            (SettingEditor::Enum(choices), CanonicalValue::Enum(value))
+                if !choices.contains(&value.as_str()) =>
+            {
+                return Err(input_error(format!(
+                    "Invalid choice for {}",
+                    definition.id
+                )));
+            }
+            (SettingEditor::Language, CanonicalValue::Text(value))
+                if value.is_empty()
+                    || value.len() > 64
+                    || value.chars().any(char::is_control) =>
+            {
+                return Err(input_error("Invalid language value"));
+            }
+            (SettingEditor::KeyBinding, CanonicalValue::KeyBinding(value))
+                if value.len() > 256
+                    || value.contains(['\r', '\n'])
+                    || !valid_modern_key_binding(value) =>
+            {
+                return Err(input_error("Invalid key binding value"));
+            }
+            _ => {}
+        }
+    } else if let CanonicalValue::ExternalRaw(raw) = value {
+        validate_raw_key_value("external", raw)?;
+    } else {
+        return Err(input_error("Custom settings require a raw string value"));
+    }
+    Ok(())
+}
+
+pub(in crate::api::instance) fn validate_canonical_value(
+    definition: Option<&SupportedSetting>,
+    value: &CanonicalValue,
+) -> crate::Result<()> {
+    validate_value(definition, value, true)
+}
+
+pub(in crate::api::instance) fn validate_file_value(
+    definition: Option<&SupportedSetting>,
+    value: &CanonicalValue,
+) -> crate::Result<()> {
+    validate_value(definition, value, false)
+}
+
+pub(in crate::api::instance) fn decode_value_for_version(
+    definition: &SupportedSetting,
+    physical_key: &str,
+    raw: &str,
+    game_version: &str,
+) -> Option<CanonicalValue> {
+    if !setting_available_for_version(definition, game_version) {
+        return None;
+    }
+    let value = decode_value(definition, physical_key, raw)?;
+    validate_file_value(Some(definition), &value).ok()?;
+    let target_key = if definition.versioned_keys.is_empty() {
+        physical_key
+    } else {
+        physical_variant_for_version(definition, game_version)?.key
+    };
+    encode_value(definition, target_key, &value, game_version, None)?;
+    Some(value)
+}
+
+pub(in crate::api::instance) fn target_physical_key(
+    definition: Option<&SupportedSetting>,
+    stored: &StoredOption,
+    document: &GameOptionsDocument,
+    game_version: &str,
+) -> Option<String> {
+    if let Some(definition) = definition {
+        if !setting_available_for_version(definition, game_version) {
+            return None;
+        }
+        if !definition.versioned_keys.is_empty() {
+            observed_physical_key(definition, document, game_version)?;
+            return physical_variant_for_version(definition, game_version)
+                .map(|variant| variant.key.to_string());
+        }
+        definition
+            .keys
+            .iter()
+            .find(|key| document.value(key).is_some())
+            .map(|key| (*key).to_string())
+    } else {
+        stored.raw_key.clone()
+    }
+}
+
+pub(in crate::api::instance) fn observed_physical_key(
+    definition: &SupportedSetting,
+    document: &GameOptionsDocument,
+    game_version: &str,
+) -> Option<String> {
+    if !setting_available_for_version(definition, game_version) {
+        return None;
+    }
+    if let Some(target) = physical_variant_for_version(definition, game_version)
+        && document.value(target.key).is_some()
+    {
+        return Some(target.key.to_string());
+    }
+    definition
+        .keys
+        .iter()
+        .find(|key| document.value(key).is_some())
+        .map(|key| (*key).to_string())
+}
+
+pub(in crate::api::instance) fn alias_migration_needed(
+    definition: &SupportedSetting,
+    document: &GameOptionsDocument,
+    target_key: &str,
+) -> bool {
+    document.value(target_key).is_none()
+        && definition
+            .keys
+            .iter()
+            .any(|key| *key != target_key && document.value(key).is_some())
+}
+
+pub(in crate::api::instance) fn physical_representation_supported_for_target(
+    definition: &SupportedSetting,
+    physical_key: &str,
+    raw: &str,
+    game_version: &str,
+) -> bool {
+    if !setting_available_for_version(definition, game_version) {
+        return false;
+    }
+    let Some(target_version) = release_version(game_version) else {
+        return false;
+    };
+    if matches!(definition.encoding, ValueEncoding::KeyBinding) {
+        return if target_version >= (1, 13, 0) {
+            valid_modern_key_binding(raw)
+        } else {
+            legacy_key_binding_to_token(raw).is_some()
+        };
+    }
+    if matches!(definition.encoding, ValueEncoding::AmbientOcclusion) {
+        return if ((1, 5, 1)..=(1, 19, 2)).contains(&target_version) {
+            matches!(raw, "0" | "1" | "2")
+        } else {
+            matches!(raw, "true" | "false")
+        };
+    }
+    if matches!(definition.encoding, ValueEncoding::Fov) {
+        return raw.parse::<f64>().is_ok_and(|value| {
+            value.is_finite() && (-1.0..=1.0).contains(&value)
+        });
+    }
+    if matches!(definition.encoding, ValueEncoding::ChatPreview) {
+        return if target_version == (1, 19, 0) {
+            matches!(raw, "true" | "false")
+        } else {
+            matches!(raw, "0" | "1" | "2")
+        };
+    }
+    if matches!(definition.encoding, ValueEncoding::GuiScale) {
+        return raw.parse::<i64>().is_ok_and(|value| {
+            if target_version >= (1, 13, 0) {
+                (0..=8).contains(&value)
+            } else {
+                (0..=3).contains(&value)
+            }
+        });
+    }
+    if matches!(definition.encoding, ValueEncoding::MenuBackgroundBlur) {
+        return if target_version >= (1, 21, 0) {
+            raw.parse::<i64>()
+                .is_ok_and(|value| (0..=10).contains(&value))
+        } else {
+            raw.parse::<f64>().is_ok_and(|value| {
+                value.is_finite()
+                    && value.fract() == 0.0
+                    && (0.0..=10.0).contains(&value)
+            })
+        };
+    }
+    if matches!(definition.encoding, ValueEncoding::Clouds) {
+        return if target_version <= (1, 8, 0) {
+            matches!(raw, "true" | "false")
+        } else {
+            decode_string_token(raw)
+                .is_some_and(|value| CLOUD_VALUES.contains(&value.as_str()))
+        };
+    }
+
+    let mut variants = definition
+        .versioned_keys
+        .iter()
+        .filter(|variant| variant.key == physical_key)
+        .peekable();
+    if variants.peek().is_none() {
+        return true;
+    }
+    variants.any(|variant| {
+        release_version(variant.since)
+            .is_some_and(|since| since <= target_version)
+            && release_version(variant.until)
+                .is_some_and(|until| target_version <= until)
+    })
+}
+
+pub(in crate::api::instance) fn format_decimal(value: f64) -> String {
+    let value = format!("{value:.8}");
+    let value = value.trim_end_matches('0').trim_end_matches('.');
+    if value == "-0" {
+        "0".to_string()
+    } else {
+        value.to_string()
+    }
+}
@@ -0,0 +1,450 @@
+use super::{
+    BOOL, SettingEditor, SupportedSetting, UNIT_INTERVAL, ValueEncoding,
+    ranged_setting, setting, version_changes, versioned_setting,
+};
+
+const GRAPHICS: &[&str] = &["fast", "fancy", "fabulous", "custom"];
+const AMBIENT_OCCLUSION: &[&str] = &["off", "on", "minimum", "maximum"];
+const PARTICLES: &[&str] = &["0", "1", "2"];
+const CLOUDS: &[&str] = &["false", "fast", "true"];
+const ATTACK_INDICATOR: &[&str] = &["0", "1", "2"];
+const INACTIVITY_FPS_LIMIT: &[&str] = &["afk", "minimized"];
+const PRIORITIZE_CHUNK_UPDATES: &[&str] = &["0", "1", "2"];
+const TEXTURE_FILTERING: &[&str] = &["0", "1", "2"];
+const GRAPHICS_BACKEND: &[&str] = &["default", "opengl", "vulkan"];
+const LEGACY_FPS_LIMIT: &[&str] = &["0", "1", "2"];
+const LEGACY_VIEW_DISTANCE: &[&str] = &["0", "1", "2", "3"];
+
+pub(super) const SETTINGS: &[SupportedSetting] = &[
+    versioned_setting(
+        "fov",
+        &["fov"],
+        version_changes::FOV_KEYS,
+        "video",
+        true,
+        SettingEditor::Integer {
+            min: 30,
+            max: 110,
+            step: 1,
+        },
+        ValueEncoding::Fov,
+    ),
+    versioned_setting(
+        "graphics",
+        &["graphicsPreset", "graphicsMode", "fancyGraphics"],
+        version_changes::GRAPHICS_KEYS,
+        "video",
+        true,
+        SettingEditor::Enum(GRAPHICS),
+        ValueEncoding::Graphics,
+    ),
+    versioned_setting(
+        "ambient_occlusion",
+        &["ao"],
+        version_changes::AMBIENT_OCCLUSION_KEYS,
+        "video",
+        true,
+        SettingEditor::Enum(AMBIENT_OCCLUSION),
+        ValueEncoding::AmbientOcclusion,
+    ),
+    setting(
+        "brightness",
+        &["gamma"],
+        "video",
+        true,
+        UNIT_INTERVAL,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "render_distance",
+        &["renderDistance"],
+        "1.7.2",
+        "26.3",
+        "video",
+        false,
+        SettingEditor::Integer {
+            min: 2,
+            max: 64,
+            step: 1,
+        },
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "legacy_view_distance",
+        &["viewDistance"],
+        "1.0",
+        "1.6.4",
+        "video",
+        false,
+        SettingEditor::Enum(LEGACY_VIEW_DISTANCE),
+        ValueEncoding::Enum(LEGACY_VIEW_DISTANCE),
+    ),
+    ranged_setting(
+        "simulation_distance",
+        &["simulationDistance"],
+        "1.18",
+        "26.3",
+        "video",
+        false,
+        SettingEditor::Integer {
+            min: 2,
+            max: 64,
+            step: 1,
+        },
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "entity_distance",
+        &["entityDistanceScaling"],
+        "1.16",
+        "26.3",
+        "video",
+        false,
+        SettingEditor::Decimal {
+            min: 0.5,
+            max: 5.0,
+            step: 0.25,
+            unit: Some("multiplier"),
+        },
+        ValueEncoding::Decimal,
+    ),
+    setting(
+        "gui_scale",
+        &["guiScale"],
+        "video",
+        true,
+        SettingEditor::Integer {
+            min: 0,
+            max: 8,
+            step: 1,
+        },
+        ValueEncoding::GuiScale,
+    ),
+    ranged_setting(
+        "debug_gui_scale",
+        &["debugGuiScale"],
+        "26.3",
+        "26.3",
+        "video",
+        true,
+        SettingEditor::UnboundedInteger,
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "graphics_backend",
+        &["preferredGraphicsBackend"],
+        "26.2",
+        "26.3",
+        "video",
+        false,
+        SettingEditor::Enum(GRAPHICS_BACKEND),
+        ValueEncoding::QuotedEnum(GRAPHICS_BACKEND),
+    ),
+    setting(
+        "particles",
+        &["particles"],
+        "video",
+        true,
+        SettingEditor::Enum(PARTICLES),
+        ValueEncoding::Enum(PARTICLES),
+    ),
+    versioned_setting(
+        "clouds",
+        &["renderClouds", "clouds"],
+        version_changes::CLOUD_KEYS,
+        "video",
+        true,
+        SettingEditor::Enum(CLOUDS),
+        ValueEncoding::Clouds,
+    ),
+    ranged_setting(
+        "cloud_range",
+        &["cloudRange"],
+        "1.21.6",
+        "26.3",
+        "video",
+        false,
+        SettingEditor::UnboundedInteger,
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "entity_shadows",
+        &["entityShadows"],
+        "1.8.1",
+        "26.3",
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    setting(
+        "view_bobbing",
+        &["bobView"],
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "vsync",
+        &["enableVsync"],
+        "1.3.1",
+        "26.3",
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "fullscreen",
+        &["fullscreen"],
+        "1.3.1",
+        "26.3",
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "exclusive_fullscreen",
+        &["exclusiveFullscreen"],
+        "26.1",
+        "26.3",
+        "video",
+        false,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "mac_fullscreen_menu",
+        &["macFullscreenMenuVisibility"],
+        "26.3",
+        "26.3",
+        "video",
+        false,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "max_framerate",
+        &["maxFps"],
+        "1.7.2",
+        "26.3",
+        "video",
+        true,
+        SettingEditor::Integer {
+            min: 10,
+            max: 260,
+            step: 10,
+        },
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "legacy_framerate_limit",
+        &["fpsLimit"],
+        "1.0",
+        "1.6.4",
+        "video",
+        false,
+        SettingEditor::Enum(LEGACY_FPS_LIMIT),
+        ValueEncoding::Enum(LEGACY_FPS_LIMIT),
+    ),
+    ranged_setting(
+        "inactivity_framerate_limit",
+        &["inactivityFpsLimit"],
+        "1.21.2",
+        "26.3",
+        "video",
+        true,
+        SettingEditor::Enum(INACTIVITY_FPS_LIMIT),
+        ValueEncoding::QuotedEnum(INACTIVITY_FPS_LIMIT),
+    ),
+    ranged_setting(
+        "mipmap_levels",
+        &["mipmapLevels"],
+        "1.7.2",
+        "26.3",
+        "video",
+        false,
+        SettingEditor::Integer {
+            min: 0,
+            max: 4,
+            step: 1,
+        },
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "biome_blend_radius",
+        &["biomeBlendRadius"],
+        "1.13",
+        "26.3",
+        "video",
+        true,
+        SettingEditor::Integer {
+            min: 0,
+            max: 7,
+            step: 1,
+        },
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "prioritize_chunk_updates",
+        &["prioritizeChunkUpdates"],
+        "1.18",
+        "26.3",
+        "video",
+        true,
+        SettingEditor::Enum(PRIORITIZE_CHUNK_UPDATES),
+        ValueEncoding::Enum(PRIORITIZE_CHUNK_UPDATES),
+    ),
+    ranged_setting(
+        "attack_indicator",
+        &["attackIndicator"],
+        "1.9",
+        "26.3",
+        "video",
+        true,
+        SettingEditor::Enum(ATTACK_INDICATOR),
+        ValueEncoding::Enum(ATTACK_INDICATOR),
+    ),
+    ranged_setting(
+        "reduced_debug_info",
+        &["reducedDebugInfo"],
+        "1.8",
+        "26.3",
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "chunk_fade_time",
+        &["chunkSectionFadeInTime"],
+        "1.21.11",
+        "26.3",
+        "video",
+        false,
+        SettingEditor::UnboundedDecimal,
+        ValueEncoding::Decimal,
+    ),
+    ranged_setting(
+        "cutout_leaves",
+        &["cutoutLeaves"],
+        "1.21.11",
+        "26.3",
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "improved_transparency",
+        &["improvedTransparency"],
+        "1.21.11",
+        "26.3",
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "texture_filtering",
+        &["textureFiltering"],
+        "1.21.11",
+        "26.3",
+        "video",
+        false,
+        SettingEditor::Enum(TEXTURE_FILTERING),
+        ValueEncoding::Enum(TEXTURE_FILTERING),
+    ),
+    ranged_setting(
+        "anisotropy",
+        &["maxAnisotropyBit"],
+        "1.21.11",
+        "26.3",
+        "video",
+        false,
+        SettingEditor::UnboundedInteger,
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "vignette",
+        &["vignette"],
+        "1.21.11",
+        "26.3",
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "weather_radius",
+        &["weatherRadius"],
+        "1.21.11",
+        "26.3",
+        "video",
+        false,
+        SettingEditor::UnboundedInteger,
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "advanced_opengl",
+        &["advancedOpengl"],
+        "1.0",
+        "1.7.10",
+        "video",
+        false,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "anaglyph_3d",
+        &["anaglyph3d"],
+        "1.0",
+        "1.12.2",
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "anisotropic_filtering",
+        &["anisotropicFiltering"],
+        "1.7.2",
+        "1.7.10",
+        "video",
+        false,
+        SettingEditor::UnboundedInteger,
+        ValueEncoding::Integer,
+    ),
+    ranged_setting(
+        "alternate_blocks",
+        &["allowBlockAlternatives"],
+        "1.8",
+        "1.8.9",
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "held_item_tooltips",
+        &["heldItemTooltips"],
+        "1.4.6",
+        "1.19.3",
+        "video",
+        true,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+    ranged_setting(
+        "use_vbo",
+        &["useVbo"],
+        "1.8",
+        "1.13.2",
+        "video",
+        false,
+        BOOL,
+        ValueEncoding::Bool,
+    ),
+];
@@ -0,0 +1,149 @@
+//! Keeps the app-wide fullscreen setting aligned with the shared Minecraft value.
+
+use super::CATALOG_REVISION;
+use crate::state::{
+    CanonicalValue, State, load_game_option_preferences,
+    load_game_options_sync_state, load_shared_game_options,
+};
+use chrono::Utc;
+use sqlx::{Sqlite, Transaction};
+
+const FULLSCREEN_OPTION_ID: &str = "fullscreen";
+
+pub(crate) async fn shared_fullscreen_value(
+    state: &State,
+) -> crate::Result<Option<bool>> {
+    let preferences = load_game_option_preferences(&state.pool).await?;
+    if !preferences
+        .get(FULLSCREEN_OPTION_ID)
+        .is_some_and(|preference| preference.enabled)
+    {
+        return Ok(None);
+    }
+    let values = load_shared_game_options(&state.pool).await?;
+    Ok(values.get(FULLSCREEN_OPTION_ID).and_then(|stored| {
+        if !stored.seeded {
+            return None;
+        }
+        match stored.value.as_ref() {
+            Some(CanonicalValue::Bool(value)) => Some(*value),
+            _ => None,
+        }
+    }))
+}
+
+pub(crate) async fn update_shared_fullscreen_from_app(
+    state: &State,
+    value: bool,
+) -> crate::Result<bool> {
+    let values = load_shared_game_options(&state.pool).await?;
+    let preferences = load_game_option_preferences(&state.pool).await?;
+    let stored = values.get(FULLSCREEN_OPTION_ID);
+    let preference = preferences.get(FULLSCREEN_OPTION_ID);
+    let value_matches = stored.is_some_and(|stored| {
+        stored.seeded
+            && matches!(
+                stored.value.as_ref(),
+                Some(CanonicalValue::Bool(current)) if *current == value
+            )
+    });
+    let sync_enabled = preference.is_some_and(|preference| preference.enabled);
+    if !sync_enabled || value_matches {
+        return Ok(false);
+    }
+
+    let option_revision = stored
+        .map(|stored| stored.revision)
+        .unwrap_or(0)
+        .max(
+            preference
+                .map(|preference| preference.revision)
+                .unwrap_or(0),
+        )
+        .saturating_add(1) as i64;
+    let (canonical_revision, _) =
+        load_game_options_sync_state(&state.pool, CATALOG_REVISION).await?;
+    let next_canonical_revision = canonical_revision.saturating_add(1) as i64;
+    let canonical = CanonicalValue::Bool(value);
+    let value_json = serde_json::to_string(&canonical)?;
+    let canonical_type = canonical.type_name();
+    let now = Utc::now().timestamp();
+    let catalog_revision = CATALOG_REVISION as i64;
+    let kind = "vanilla";
+    let raw_key: Option<&str> = None;
+    let value_codec = "catalog";
+    let source_game_version: Option<&str> = None;
+    let mut tx = state.pool.begin().await?;
+
+    sqlx::query(
+        "INSERT INTO synced_game_option_values
+            (option_id, kind, raw_key, canonical_type,
+             canonical_value_json, value_codec, seeded, revision, origin,
+             source_game_version, source_instance_id, updated_at)
+        VALUES (?, ?, ?, ?, ?, ?, 1, ?, 'app_editor', ?, NULL, ?)
+        ON CONFLICT(option_id) DO UPDATE SET
+            kind = excluded.kind, raw_key = excluded.raw_key,
+            canonical_type = excluded.canonical_type,
+            canonical_value_json = excluded.canonical_value_json,
+            value_codec = excluded.value_codec, seeded = 1,
+            revision = excluded.revision, origin = 'app_editor',
+            source_game_version = NULL, source_instance_id = NULL,
+            updated_at = excluded.updated_at",
+    )
+    .bind(FULLSCREEN_OPTION_ID)
+    .bind(kind)
+    .bind(raw_key)
+    .bind(canonical_type)
+    .bind(value_json)
+    .bind(value_codec)
+    .bind(option_revision)
+    .bind(source_game_version)
+    .bind(now)
+    .execute(&mut *tx)
+    .await?;
+    sqlx::query(
+        "INSERT INTO synced_game_option_preferences
+            (option_id, enabled, source, revision)
+        VALUES (?, ?, ?, ?)
+        ON CONFLICT(option_id) DO UPDATE SET
+            enabled = excluded.enabled, source = 'user',
+            revision = excluded.revision",
+    )
+    .bind(FULLSCREEN_OPTION_ID)
+    .bind(true)
+    .bind("user")
+    .bind(option_revision)
+    .execute(&mut *tx)
+    .await?;
+    sqlx::query(
+        "INSERT INTO synced_game_option_state (singleton, revision, catalog_revision)
+        VALUES (1, ?, ?)
+        ON CONFLICT(singleton) DO UPDATE SET
+            revision = excluded.revision,
+            catalog_revision = excluded.catalog_revision",
+    )
+    .bind(next_canonical_revision)
+    .bind(catalog_revision)
+    .execute(&mut *tx)
+    .await?;
+    tx.commit().await?;
+    Ok(true)
+}
+
+pub(super) async fn update_app_fullscreen_setting(
+    tx: &mut Transaction<'_, Sqlite>,
+    value: &CanonicalValue,
+    sync_enabled: bool,
+) -> crate::Result<()> {
+    if !sync_enabled {
+        return Ok(());
+    }
+    let CanonicalValue::Bool(value) = value else {
+        return Ok(());
+    };
+    sqlx::query("UPDATE settings SET mc_force_fullscreen = ? WHERE id = 0")
+        .bind(*value)
+        .execute(&mut **tx)
+        .await?;
+    Ok(())
+}
@@ -0,0 +1,498 @@
+//! Works out which instances can receive each shared setting.
+
+use super::super as synced_options;
+use super::CATALOG_REVISION;
+use super::api_types::*;
+use super::catalog::*;
+use super::options_file::{
+    GameOptionsDocument, options_path, read_document, sha1_bytes,
+};
+use crate::state::{
+    CanonicalValue, InstanceMetadata, State, StoredOption,
+    game_options_sync_is_enabled,
+};
+use std::collections::BTreeMap;
+
+/// The instance data needed to decide whether a setting can be synced.
+#[derive(Clone)]
+pub(super) struct ParticipatingInstance {
+    metadata: InstanceMetadata,
+    deferred: bool,
+    fullscreen_controlled: bool,
+    pub(super) document: Option<GameOptionsDocument>,
+    inspection_error: Option<String>,
+}
+
+/// Loads every instance with game-settings sync turned on.
+///
+/// An instance may not have an `options.txt` until its first launch. It still takes
+/// part in sync, but its settings are marked as waiting for the file.
+pub(super) async fn load_participating_instances(
+    state: &State,
+) -> crate::Result<Vec<ParticipatingInstance>> {
+    if !game_options_sync_is_enabled(&state.pool).await? {
+        return Ok(Vec::new());
+    }
+    let instances = crate::state::list_instances(&state.pool).await?;
+    let mut participants = Vec::new();
+    for metadata in instances {
+        if !metadata.synced_options.game_options {
+            continue;
+        }
+        let deferred = synced_options::sync_files_are_protected(&metadata)
+            || synced_options::pending::contains(
+                &metadata.instance.id,
+                crate::state::SyncedOption::GameOptions,
+                state,
+            )
+            .await?;
+        let path = options_path(&metadata, state)?;
+        let (document, inspection_error) = if path.exists() {
+            match read_document(&path).await {
+                Ok((document, _)) => (Some(document), None),
+                Err(error) => {
+                    tracing::warn!(
+                        "Could not inspect game options compatibility for {}: {error}",
+                        metadata.instance.id
+                    );
+                    (None, Some(error.to_string()))
+                }
+            }
+        } else {
+            (None, None)
+        };
+        participants.push(ParticipatingInstance {
+            fullscreen_controlled: metadata
+                .launch_overrides
+                .force_fullscreen
+                .is_some(),
+            metadata,
+            deferred,
+            document,
+            inspection_error,
+        });
+    }
+    Ok(participants)
+}
+
+pub(super) fn summary_revision(
+    canonical_revision: u64,
+    participants: &[ParticipatingInstance],
+) -> String {
+    let mut summary = format!("{CATALOG_REVISION}:{canonical_revision}");
+    let mut participants = participants.iter().collect::<Vec<_>>();
+    participants.sort_by(|left, right| {
+        left.metadata.instance.id.cmp(&right.metadata.instance.id)
+    });
+    for participant in participants {
+        summary.push('|');
+        summary.push_str(&participant.metadata.instance.id);
+        summary.push(':');
+        summary
+            .push_str(&participant.metadata.applied_content_set.game_version);
+        summary.push(':');
+        summary.push_str(if participant.deferred {
+            "deferred"
+        } else {
+            "ready"
+        });
+        summary.push(':');
+        summary.push_str(if participant.inspection_error.is_some() {
+            "degraded"
+        } else if participant.document.is_some() {
+            "file"
+        } else {
+            "missing"
+        });
+        summary.push(':');
+        summary.push_str(if participant.fullscreen_controlled {
+            "fullscreen-controlled"
+        } else {
+            "fullscreen-shared"
+        });
+    }
+    sha1_bytes(summary.as_bytes())
+}
+/// Counts which instances can receive a setting now, later, or not at all.
+///
+/// The settings screen uses these results for its preview, and the file writer uses
+/// the same checks when it saves. A setting shown as blocked therefore cannot be
+/// written behind the user's back.
+pub(super) fn describe_instance_support(
+    definition: Option<&SupportedSetting>,
+    stored: &StoredOption,
+    value: Option<&CanonicalValue>,
+    participants: &[ParticipatingInstance],
+) -> GameOptionCompatibility {
+    let total = participants.len() as u32;
+    let mut will_receive = 0;
+    let mut write_now = 0;
+    let mut buckets: BTreeMap<
+        (String, String, String, String),
+        GameOptionCompatibilityBucket,
+    > = BTreeMap::new();
+
+    for participant in participants {
+        let version = participant
+            .metadata
+            .applied_content_set
+            .game_version
+            .clone();
+        // Check launcher-controlled settings first. Finding the key in options.txt
+        // does not make a launcher-owned setting safe to overwrite.
+        let (status, key, mapping, reason) = if stored.option_id == "fullscreen"
+            && participant.fullscreen_controlled
+        {
+            (
+                GameOptionCompatibilityStatus::Controlled,
+                None,
+                None,
+                Some(GameOptionCompatibilityReason::LauncherControlled),
+            )
+        } else if definition.is_some()
+            && !supported_settings_cover_game_version(&version)
+        {
+            (
+                GameOptionCompatibilityStatus::CatalogUncovered,
+                None,
+                None,
+                Some(GameOptionCompatibilityReason::CatalogUncovered),
+            )
+        } else if participant.inspection_error.is_some() {
+            (
+                GameOptionCompatibilityStatus::Degraded,
+                None,
+                None,
+                Some(GameOptionCompatibilityReason::InspectionFailed),
+            )
+        } else {
+            match &participant.document {
+                None => {
+                    // An instance that has not launched yet has no options.txt. If we know
+                    // the key Minecraft will create, wait for the file instead of excluding it.
+                    if definition.is_none()
+                        && stored.raw_key.is_some()
+                        && matches!(value, Some(CanonicalValue::ExternalRaw(_)))
+                    {
+                        (
+						GameOptionCompatibilityStatus::WaitingForFile,
+						stored.raw_key.clone(),
+						Some(GameOptionMappingKind::Direct),
+						Some(GameOptionCompatibilityReason::WaitingForOptionsFile),
+					)
+                    } else if let Some((key, mapping)) =
+                        definition.and_then(|definition| {
+                            target_key_for_version(definition, &version).map(
+                                |key| {
+                                    let mapping = physical_variant_for_version(
+                                        definition, &version,
+                                    )
+                                    .map(|variant| variant.mapping)
+                                    .unwrap_or(GameOptionMappingKind::Direct);
+                                    (key, mapping)
+                                },
+                            )
+                        })
+                    {
+                        let representable = value.is_none_or(|value| {
+                            definition.is_some_and(|definition| {
+                                encode_value(
+                                    definition, key, value, &version, None,
+                                )
+                                .is_some()
+                            })
+                        });
+                        if representable {
+                            (
+							GameOptionCompatibilityStatus::WaitingForFile,
+							Some(key.to_string()),
+							Some(mapping),
+							Some(GameOptionCompatibilityReason::WaitingForOptionsFile),
+						)
+                        } else {
+                            (
+							GameOptionCompatibilityStatus::UnsupportedValue,
+							Some(key.to_string()),
+							None,
+							Some(GameOptionCompatibilityReason::UnsupportedValue),
+						)
+                        }
+                    } else {
+                        (
+                            GameOptionCompatibilityStatus::NotAvailable,
+                            None,
+                            None,
+                            Some(GameOptionCompatibilityReason::MissingSetting),
+                        )
+                    }
+                }
+                Some(document) => {
+                    // Vanilla keys sometimes change between versions. Replace an old key with
+                    // its newer name only when we know the value can be converted safely.
+                    let key = target_physical_key(
+                        definition, stored, document, &version,
+                    );
+                    if let Some(key) = key {
+                        let needs_alias_migration =
+                            definition.is_some_and(|definition| {
+                                alias_migration_needed(
+                                    definition, document, &key,
+                                )
+                            });
+                        let representable =
+                            value.is_none_or(|value| match definition {
+                                Some(definition) => encode_value(
+                                    definition,
+                                    &key,
+                                    value,
+                                    &version,
+                                    document.value(&key),
+                                )
+                                .is_some(),
+                                None => matches!(
+                                    value,
+                                    CanonicalValue::ExternalRaw(_)
+                                ),
+                            });
+                        if !representable {
+                            (
+							GameOptionCompatibilityStatus::UnsupportedValue,
+							Some(key.to_string()),
+							None,
+							Some(GameOptionCompatibilityReason::UnsupportedValue),
+						)
+                        } else {
+                            let mapped = if needs_alias_migration {
+                                Some(GameOptionMappingKind::Migrated)
+                            } else {
+                                definition.and_then(|definition| {
+                                    physical_variant_for_present_key(
+                                        definition, &key, &version,
+                                    )
+                                    .map(|variant| variant.mapping)
+                                    .or_else(|| {
+                                        (matches!(
+                                            definition.encoding,
+                                            ValueEncoding::KeyBinding
+                                        ) && document.value(&key).is_some_and(
+                                            |raw| {
+                                                split_key_binding(raw)
+                                                    .0
+                                                    .parse::<i32>()
+                                                    .is_ok()
+                                            },
+                                        ))
+                                        .then_some(
+                                            GameOptionMappingKind::Migrated,
+                                        )
+                                    })
+                                })
+                            };
+                            let legacy = definition.is_some_and(|definition| {
+                                definition.keys.first().copied()
+                                    != Some(key.as_str())
+                            });
+                            (
+							if participant.deferred {
+								GameOptionCompatibilityStatus::Deferred
+							} else {
+								GameOptionCompatibilityStatus::Ready
+							},
+							Some(key.to_string()),
+							Some(mapped.unwrap_or(if legacy {
+								GameOptionMappingKind::Legacy
+							} else {
+								GameOptionMappingKind::Direct
+							})),
+							needs_alias_migration
+								.then_some(GameOptionCompatibilityReason::MigratesOnWrite),
+						)
+                        }
+                    } else if let Some(definition) =
+                        definition.filter(|definition| {
+                            setting_available_for_version(definition, &version)
+                                && definition
+                                    .keys
+                                    .iter()
+                                    .any(|key| document.value(key).is_some())
+                        })
+                    {
+                        let eventual_key =
+                            target_key_for_version(definition, &version)
+                                .map(str::to_string);
+                        let representable =
+                            eventual_key.as_deref().is_some_and(|key| {
+                                value.is_none_or(|value| {
+                                    encode_value(
+                                        definition, key, value, &version, None,
+                                    )
+                                    .is_some()
+                                })
+                            });
+                        if representable {
+                            (
+							GameOptionCompatibilityStatus::WaitingForBase,
+							eventual_key,
+							Some(GameOptionMappingKind::Migrated),
+							Some(GameOptionCompatibilityReason::WaitingForCompatibleBase),
+						)
+                        } else {
+                            (
+							GameOptionCompatibilityStatus::UnsupportedValue,
+							eventual_key,
+							None,
+							Some(GameOptionCompatibilityReason::UnsupportedValue),
+						)
+                        }
+                    } else {
+                        (
+                            GameOptionCompatibilityStatus::NotAvailable,
+                            None,
+                            None,
+                            Some(GameOptionCompatibilityReason::MissingSetting),
+                        )
+                    }
+                }
+            }
+        };
+
+        let receives = matches!(
+            status,
+            GameOptionCompatibilityStatus::Ready
+                | GameOptionCompatibilityStatus::Deferred
+                | GameOptionCompatibilityStatus::WaitingForFile
+                | GameOptionCompatibilityStatus::WaitingForBase
+        );
+        if receives {
+            will_receive += 1;
+        }
+        if matches!(status, GameOptionCompatibilityStatus::Ready) {
+            write_now += 1;
+        }
+        let status_key = serde_json::to_string(&status).unwrap_or_default();
+        let key_name = key.clone().unwrap_or_default();
+        let mapping_key = mapping
+            .as_ref()
+            .and_then(|mapping| serde_json::to_string(mapping).ok())
+            .unwrap_or_default();
+        let reason_key = reason
+            .as_ref()
+            .and_then(|reason| serde_json::to_string(reason).ok())
+            .unwrap_or_default();
+        // Group instances with the same result to keep the response small. Keep their
+        // Minecraft versions so the UI can explain which versions are affected.
+        let bucket = buckets
+            .entry((status_key, key_name.clone(), mapping_key, reason_key))
+            .or_insert_with(|| GameOptionCompatibilityBucket {
+                instance_count: 0,
+                write_keys: if matches!(
+                    status,
+                    GameOptionCompatibilityStatus::Ready
+                        | GameOptionCompatibilityStatus::Deferred
+                ) {
+                    key.clone().into_iter().collect()
+                } else {
+                    Vec::new()
+                },
+                eventual_keys: if matches!(
+                    status,
+                    GameOptionCompatibilityStatus::WaitingForFile
+                        | GameOptionCompatibilityStatus::WaitingForBase
+                ) {
+                    key.clone().into_iter().collect()
+                } else {
+                    Vec::new()
+                },
+                game_versions: vec![version.clone()],
+                status,
+                mapping,
+                reason,
+            });
+        bucket.instance_count += 1;
+        if !bucket.game_versions.contains(&version) {
+            bucket.game_versions.push(version);
+            bucket.game_versions.sort();
+        }
+    }
+
+    let left_local = total.saturating_sub(will_receive);
+    GameOptionCompatibility {
+        total_participating: total,
+        will_receive,
+        write_now,
+        left_local,
+        buckets: buckets.into_values().collect(),
+    }
+}
+
+/// Uses the local value only when every readable instance currently agrees on it.
+pub(super) fn find_common_local_value(
+    definition: Option<&SupportedSetting>,
+    stored: &StoredOption,
+    participants: &[ParticipatingInstance],
+) -> (Option<CanonicalValue>, GameOptionValueState) {
+    let mut values = Vec::new();
+    let mut invalid = false;
+    for participant in participants {
+        if stored.option_id == "fullscreen" && participant.fullscreen_controlled
+        {
+            continue;
+        }
+        if definition.is_some()
+            && !supported_settings_cover_game_version(
+                &participant.metadata.applied_content_set.game_version,
+            )
+        {
+            continue;
+        }
+        let Some(document) = &participant.document else {
+            continue;
+        };
+        let key = if let Some(definition) = definition {
+            observed_physical_key(
+                definition,
+                document,
+                &participant.metadata.applied_content_set.game_version,
+            )
+        } else {
+            target_physical_key(
+                None,
+                stored,
+                document,
+                &participant.metadata.applied_content_set.game_version,
+            )
+        };
+        let Some(key) = key else {
+            continue;
+        };
+        let Some(raw_value) = document.value(&key) else {
+            continue;
+        };
+        let value = if let Some(definition) = definition {
+            decode_value(definition, &key, raw_value)
+        } else {
+            Some(CanonicalValue::ExternalRaw(raw_value.to_string()))
+        };
+        if let Some(value) =
+            value.filter(|value| validate_file_value(definition, value).is_ok())
+        {
+            values.push(value);
+        } else {
+            invalid = true;
+        }
+    }
+    if invalid && values.is_empty() {
+        return (None, GameOptionValueState::Invalid);
+    }
+    let Some(first) = values.first().cloned() else {
+        return (None, GameOptionValueState::Unset);
+    };
+    if values
+        .iter()
+        .all(|value| canonical_values_equal(value, &first))
+    {
+        (Some(first), GameOptionValueState::UniformLocal)
+    } else {
+        (None, GameOptionValueState::Mixed)
+    }
+}
@@ -0,0 +1,76 @@
+//! Writes synced settings and launcher overrides before Minecraft starts.
+
+use super::options_file::{
+    GameOptionsDocument, input_error, options_path, read_document, sha1_bytes,
+    validate_raw_key_value,
+};
+use super::write_shared_settings::{
+    apply_shared_settings_to_instance, remember_processed_sha,
+    sync_is_active_for_instance,
+};
+use crate::state::{InstanceMetadata, State};
+use crate::util::io;
+use std::collections::HashSet;
+
+pub(super) fn currently_launcher_owned_keys(
+    metadata: &InstanceMetadata,
+) -> HashSet<String> {
+    let mut keys = HashSet::new();
+    if metadata.launch_overrides.force_fullscreen.is_some() {
+        keys.insert("fullscreen".to_string());
+    }
+    keys
+}
+
+/// Writes canonical settings to `options.txt` before launch.
+pub async fn sync_before_launch(instance_id: &str) -> crate::Result<()> {
+    let state = State::get().await?;
+    let _guard = state.lock_synced_options().await;
+    let metadata = crate::state::get_instance(instance_id, &state.pool)
+        .await?
+        .ok_or_else(|| input_error("Unknown instance"))?;
+    if sync_is_active_for_instance(&metadata, &state).await? {
+        let _ =
+            apply_shared_settings_to_instance(&metadata, &state, false).await?;
+    }
+    Ok(())
+}
+
+/// Applies launcher settings, such as forced fullscreen, after shared settings.
+///
+/// Stores the written file's hash so the watcher ignores the app's write.
+pub async fn apply_launcher_overrides(
+    instance_id: &str,
+    overrides: &[(String, String)],
+) -> crate::Result<()> {
+    if overrides.is_empty() {
+        return Ok(());
+    }
+    let state = State::get().await?;
+    let _guard = state.lock_synced_options().await;
+    let metadata = crate::state::get_instance(instance_id, &state.pool)
+        .await?
+        .ok_or_else(|| input_error("Unknown instance"))?;
+    let path = options_path(&metadata, &state)?;
+    let (mut document, input_bytes) = if path.exists() {
+        read_document(&path).await?
+    } else {
+        (
+            GameOptionsDocument::for_instance(&metadata, &state)
+                .await?
+                .unwrap_or_else(GameOptionsDocument::empty),
+            Vec::new(),
+        )
+    };
+    for (key, value) in overrides {
+        validate_raw_key_value(key, value)?;
+        document.set(key, value, true)?;
+    }
+    let output_bytes = document.serialize()?;
+    let output_sha1 = sha1_bytes(&output_bytes);
+    if output_bytes != input_bytes {
+        io::write(&path, output_bytes).await?;
+    }
+    remember_processed_sha(instance_id, &output_sha1, &state).await?;
+    Ok(())
+}
@@ -0,0 +1,272 @@
+use super::super::options_file::{input_error, sha1_bytes};
+use serde::{Deserialize, Serialize};
+use std::collections::{BTreeMap, BTreeSet};
+use std::io::{Cursor, Read, Seek};
+use std::path::Path;
+use zip::ZipArchive;
+
+pub(super) const MAX_LANGUAGE_BYTES: usize = 4 * 1024 * 1024;
+const MAX_ARCHIVE_ENTRIES: usize = 100_000;
+const MAX_NESTED_BYTES: usize = 64 * 1024 * 1024;
+const MAX_TOTAL_BYTES: usize = 128 * 1024 * 1024;
+const MAX_NESTED_DEPTH: usize = 4;
+pub(super) type Translations = BTreeMap<String, String>;
+
+#[derive(Default, Serialize, Deserialize)]
+pub(super) struct ArchiveIndex {
+    #[serde(default)]
+    pub version: u32,
+    pub bundles: Vec<LanguageBundle>,
+}
+
+#[derive(Default, Serialize, Deserialize)]
+pub(super) struct LanguageBundle {
+    pub nested_path: String,
+    pub locales: BTreeMap<String, Translations>,
+    #[serde(default)]
+    pub deprecated: DeprecatedTranslations,
+}
+
+#[derive(Default, Serialize, Deserialize)]
+pub(super) struct DeprecatedTranslations {
+    #[serde(default)]
+    removed: Vec<String>,
+    #[serde(default)]
+    renamed: BTreeMap<String, String>,
+}
+
+impl DeprecatedTranslations {
+    pub fn apply(&self, translations: &mut Translations) {
+        for key in &self.removed {
+            translations.remove(key);
+        }
+        for (from, to) in &self.renamed {
+            if let Some(value) = translations.remove(from) {
+                translations.insert(to.clone(), value);
+            } else {
+                translations.remove(to);
+            }
+        }
+    }
+}
+
+pub(super) fn parse_language(
+    bytes: &[u8],
+    legacy: bool,
+) -> crate::Result<Translations> {
+    if bytes.len() > MAX_LANGUAGE_BYTES {
+        return Err(input_error("Minecraft language file exceeds size limit"));
+    }
+    let values: Translations = if legacy {
+        String::from_utf8_lossy(bytes)
+            .lines()
+            .filter(|line| !line.starts_with('#'))
+            .filter_map(|line| line.split_once('='))
+            .map(|(key, value)| (key.to_owned(), value.to_owned()))
+            .collect()
+    } else {
+        serde_json::from_slice::<BTreeMap<String, serde_json::Value>>(bytes)?
+            .into_iter()
+            .filter_map(|(key, value)| {
+                value.as_str().map(|s| (key, s.to_owned()))
+            })
+            .collect()
+    };
+    Ok(values
+        .into_iter()
+        .filter(|(key, value)| {
+            !key.is_empty() && key.len() <= 1024 && value.len() <= 32 * 1024
+        })
+        .collect())
+}
+
+pub(super) fn inspect(
+    path: &Path,
+    expected_hash: &str,
+) -> crate::Result<ArchiveIndex> {
+    let mut file =
+        std::fs::File::open(path).map_err(crate::util::io::IOError::from)?;
+    let mut hasher = sha1_smol::Sha1::new();
+    let mut buffer = vec![0; 64 * 1024].into_boxed_slice();
+    loop {
+        let count = file
+            .read(&mut buffer)
+            .map_err(crate::util::io::IOError::from)?;
+        if count == 0 {
+            break;
+        }
+        hasher.update(&buffer[..count]);
+    }
+    if hasher.digest().to_string() != expected_hash {
+        return Err(input_error(
+            "Locale source changed before it could be indexed",
+        ));
+    }
+    file.rewind().map_err(crate::util::io::IOError::from)?;
+    let mut index = ArchiveIndex {
+        version: 2,
+        ..Default::default()
+    };
+    let mut budget = MAX_TOTAL_BYTES;
+    let mut entries = MAX_ARCHIVE_ENTRIES;
+    inspect_archive(file, "", 0, &mut budget, &mut entries, &mut index)?;
+    Ok(index)
+}
+
+fn read_entry<R: Read + Seek>(
+    archive: &mut ZipArchive<R>,
+    name: &str,
+    limit: usize,
+    budget: &mut usize,
+) -> crate::Result<Vec<u8>> {
+    let mut entry = archive
+        .by_name(name)
+        .map_err(|e| input_error(e.to_string()))?;
+    let limit = limit.min(*budget);
+    if entry.size() > limit as u64 {
+        return Err(input_error("Locale archive entry exceeds size limit"));
+    }
+    let mut bytes = Vec::new();
+    entry
+        .by_ref()
+        .take(limit as u64 + 1)
+        .read_to_end(&mut bytes)
+        .map_err(crate::util::io::IOError::from)?;
+    if bytes.len() > limit {
+        return Err(input_error("Locale archive entry exceeds size limit"));
+    }
+    *budget -= bytes.len();
+    Ok(bytes)
+}
+
+fn inspect_archive<R: Read + Seek>(
+    reader: R,
+    nested_path: &str,
+    depth: usize,
+    budget: &mut usize,
+    entries: &mut usize,
+    index: &mut ArchiveIndex,
+) -> crate::Result<()> {
+    let mut archive =
+        ZipArchive::new(reader).map_err(|e| input_error(e.to_string()))?;
+    if archive.len() > *entries {
+        return Err(input_error("Too many entries in locale archive"));
+    }
+    *entries -= archive.len();
+    let names: BTreeSet<String> =
+        archive.file_names().map(str::to_owned).collect();
+    let mut bundle = LanguageBundle {
+        nested_path: nested_path.to_owned(),
+        ..Default::default()
+    };
+    for name in &names {
+        let parts: Vec<_> = name.split('/').collect();
+        let (namespace, filename) = match parts.as_slice() {
+            ["assets", namespace, "lang", filename] => (*namespace, *filename),
+            ["lang", filename] => ("minecraft", *filename),
+            _ => continue,
+        };
+        if filename == "deprecated.json" {
+            if namespace == "minecraft" {
+                let bytes =
+                    read_entry(&mut archive, name, MAX_LANGUAGE_BYTES, budget)?;
+                bundle.deprecated = serde_json::from_slice(&bytes)?;
+            }
+            continue;
+        }
+        let legacy = filename.ends_with(".lang");
+        let Some(locale) =
+            filename.strip_suffix(if legacy { ".lang" } else { ".json" })
+        else {
+            continue;
+        };
+        if !valid_locale(locale) {
+            continue;
+        }
+        let bytes = read_entry(&mut archive, name, MAX_LANGUAGE_BYTES, budget)?;
+        match parse_language(&bytes, legacy) {
+            Ok(values) => bundle
+                .locales
+                .entry(locale.to_ascii_lowercase())
+                .or_default()
+                .extend(values),
+            Err(error) => {
+                tracing::debug!(%name, %error, "Skipping malformed mod language file")
+            }
+        }
+    }
+    index.bundles.push(bundle);
+    let mut nested = BTreeSet::new();
+    for manifest in [
+        "fabric.mod.json",
+        "quilt.mod.json",
+        "META-INF/jarjar/metadata.json",
+    ] {
+        if !names.contains(manifest) {
+            continue;
+        }
+        let bytes =
+            read_entry(&mut archive, manifest, MAX_LANGUAGE_BYTES, budget)?;
+        let Ok(value) = serde_json::from_slice::<serde_json::Value>(&bytes)
+        else {
+            continue;
+        };
+        let jars = value
+            .get("jars")
+            .or_else(|| value.pointer("/quilt_loader/jars"));
+        for jar in jars.and_then(|v| v.as_array()).into_iter().flatten() {
+            if let Some(path) = jar
+                .as_str()
+                .or_else(|| jar.get("file").and_then(|v| v.as_str()))
+                .or_else(|| jar.get("path").and_then(|v| v.as_str()))
+            {
+                nested.insert(path.to_owned());
+            }
+        }
+    }
+    if !nested.is_empty() && depth >= MAX_NESTED_DEPTH {
+        return Err(input_error("Locale archive nesting exceeds limit"));
+    }
+    for name in nested {
+        if !names.contains(&name) || !name.ends_with(".jar") {
+            continue;
+        }
+        let bytes = read_entry(&mut archive, &name, MAX_NESTED_BYTES, budget)?;
+        let path = if nested_path.is_empty() {
+            name
+        } else {
+            format!("{nested_path}!{name}")
+        };
+        inspect_archive(
+            Cursor::new(bytes),
+            &path,
+            depth + 1,
+            budget,
+            entries,
+            index,
+        )?;
+    }
+    Ok(())
+}
+
+pub(super) fn valid_locale(locale: &str) -> bool {
+    !locale.is_empty()
+        && locale.len() <= 32
+        && locale
+            .bytes()
+            .all(|c| c.is_ascii_alphanumeric() || c == b'_')
+}
+
+pub(super) fn valid_hash(hash: &str) -> bool {
+    hash.len() == 40 && hash.bytes().all(|c| c.is_ascii_hexdigit())
+}
+
+pub(super) fn checked_bytes(
+    bytes: Vec<u8>,
+    hash: &str,
+) -> crate::Result<Vec<u8>> {
+    if sha1_bytes(&bytes) != hash {
+        return Err(input_error("Minecraft locale resource checksum mismatch"));
+    }
+    Ok(bytes)
+}
@@ -0,0 +1,581 @@
+//! Caches mod translations and remembers which JAR supplied each setting.
+
+mod archive;
+mod origins;
+mod sources;
+mod storage;
+
+use super::catalog::{is_never_sync_key, setting_by_file_key};
+use super::options_file::{
+    GameOptionsDocument, input_error, options_path, read_document,
+};
+use crate::state::{InstanceMetadata, State};
+use archive::{ArchiveIndex, Translations};
+use serde::{Deserialize, Serialize};
+use sources::{ArchiveSource, Snapshot};
+use std::collections::{BTreeMap, HashMap};
+use std::sync::{
+    Arc,
+    atomic::{AtomicBool, Ordering},
+};
+use tokio::sync::Notify;
+
+#[derive(Default)]
+pub(crate) struct GameLocaleIndexer {
+    notify: Notify,
+    started: AtomicBool,
+}
+
+#[derive(Clone, Serialize, Deserialize)]
+struct Observation {
+    snapshot: String,
+    raw_key: String,
+}
+
+#[derive(Clone, Serialize, Deserialize)]
+struct Origin {
+    instance_id: String,
+    game_version: String,
+    /// Rejects origins that older versions resolved from Minecraft instead of a mod.
+    #[serde(default, rename = "game_jar_hash", skip_serializing)]
+    legacy_game_jar_hash: Option<String>,
+    archive: ArchiveSource,
+    nested_path: String,
+    translation_key: String,
+    choices: BTreeMap<String, String>,
+}
+
+#[derive(Default, Serialize)]
+pub struct GameSettingLocaleLabels {
+    pub settings: BTreeMap<String, GameSettingLocaleLabel>,
+}
+
+#[derive(Serialize)]
+pub struct GameSettingLocaleLabel {
+    pub label: String,
+    pub choices: BTreeMap<String, String>,
+    pub source: Option<GameSettingSource>,
+}
+
+#[derive(Serialize)]
+pub struct GameSettingSource {
+    pub instance_id: String,
+    pub file_name: String,
+    pub file_path: String,
+    pub project: Option<GameSettingSourceProject>,
+}
+
+#[derive(Serialize)]
+pub struct GameSettingSourceProject {
+    pub id: String,
+    pub title: String,
+    pub icon_url: Option<String>,
+}
+
+struct Candidate {
+    snapshot_id: String,
+    snapshot: Snapshot,
+    keys: BTreeMap<String, String>,
+}
+
+pub(crate) fn queue_game_locale_index() {
+    if let Some(state) = State::get_if_initialized() {
+        tracing::info!(
+            started = state.game_locale_indexer.started.load(Ordering::Acquire),
+            "Game setting locales: indexing queued"
+        );
+        state.game_locale_indexer.notify.notify_one();
+    } else {
+        tracing::warn!(
+            "Game setting locales: cannot queue indexing before state initialization"
+        );
+    }
+}
+
+pub(crate) fn start_game_locale_indexer(state: Arc<State>) {
+    if state
+        .game_locale_indexer
+        .started
+        .swap(true, Ordering::AcqRel)
+    {
+        return;
+    }
+    tracing::info!("Game setting locales: indexer started");
+    state.game_locale_indexer.notify.notify_one();
+    tokio::spawn(async move {
+        loop {
+            state.game_locale_indexer.notify.notified().await;
+            tokio::time::sleep(std::time::Duration::from_millis(300)).await;
+            let started = std::time::Instant::now();
+            if let Err(error) = index_installed_sources(&state).await {
+                tracing::warn!(%error, "Game setting locales: indexing failed");
+            }
+            tracing::info!(
+                elapsed_ms = started.elapsed().as_millis(),
+                "Game setting locales: indexing pass finished"
+            );
+        }
+    });
+}
+
+fn mod_translation_key(raw_key: &str) -> Option<&str> {
+    if setting_by_file_key(raw_key).is_some() || is_never_sync_key(raw_key) {
+        return None;
+    }
+    raw_key.strip_prefix("key_")
+}
+
+fn document_keys(document: &GameOptionsDocument) -> BTreeMap<String, String> {
+    document
+        .effective_entries()
+        .keys()
+        .filter(|key| mod_translation_key(key).is_some())
+        .map(|key| (format!("external:{key}"), (*key).to_owned()))
+        .collect()
+}
+
+pub(super) fn has_localizable_mod_settings(
+    document: &GameOptionsDocument,
+) -> bool {
+    document
+        .effective_entries()
+        .keys()
+        .any(|key| mod_translation_key(key).is_some())
+}
+
+/// Records mod JAR hashes before saving new options.
+pub(super) async fn capture_observation(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> Option<String> {
+    match sources::snapshot_instance(metadata, state).await {
+        Ok(id) => Some(id),
+        Err(error) => {
+            tracing::warn!(%error, instance_id = metadata.instance.id,
+				"Game setting locales: snapshot capture failed");
+            None
+        }
+    }
+}
+
+pub(super) async fn record_observations(
+    tx: &mut sqlx::Transaction<'_, sqlx::Sqlite>,
+    metadata: &InstanceMetadata,
+    document: &GameOptionsDocument,
+    snapshot: Option<&str>,
+) {
+    let Some(snapshot) = snapshot else {
+        return;
+    };
+    for (id, raw_key) in document_keys(document) {
+        let observation = Observation {
+            snapshot: snapshot.to_owned(),
+            raw_key,
+        };
+        if let Err(error) = storage::observe(
+            tx,
+            "",
+            &id,
+            &metadata.instance.id,
+            &metadata.applied_content_set.game_version,
+            &observation,
+        )
+        .await
+        {
+            tracing::warn!(%error, "Could not record game-setting translation provenance");
+        }
+    }
+}
+
+async fn cached_archive(
+    state: &State,
+    source: &ArchiveSource,
+    cache: &mut HashMap<String, Arc<ArchiveIndex>>,
+) -> crate::Result<Arc<ArchiveIndex>> {
+    if let Some(index) = cache.get(&source.hash) {
+        return Ok(index.clone());
+    }
+    let index = Arc::new(sources::archive_index(state, source).await?);
+    if cache.len() >= 8 {
+        cache.clear();
+    }
+    cache.insert(source.hash.clone(), index.clone());
+    Ok(index)
+}
+
+#[tracing::instrument(skip_all, err)]
+async fn index_installed_sources(state: &State) -> crate::Result<()> {
+    let mut instances = crate::state::list_instances(&state.pool).await?;
+    tracing::info!(
+        instances = instances.len(),
+        "Game setting locales: indexing installed instances"
+    );
+    instances.sort_by(|a, b| a.instance.id.cmp(&b.instance.id));
+    let mut candidates = Vec::new();
+    let mut resolver = origins::OriginResolver::default();
+    for metadata in instances {
+        if super::super::sync_files_are_protected(&metadata) {
+            tracing::info!(
+                instance_id = metadata.instance.id,
+                "Game setting locales: skipping protected instance"
+            );
+            continue;
+        }
+        let path = match options_path(&metadata, state) {
+            Ok(path) => path,
+            Err(error) => {
+                tracing::warn!(%error, instance_id = metadata.instance.id, "Game setting locales: options path resolution failed");
+                continue;
+            }
+        };
+        let document = match read_document(&path).await {
+            Ok((document, _)) => document,
+            Err(error) => {
+                tracing::warn!(%error, instance_id = metadata.instance.id, "Game setting locales: options file read failed");
+                continue;
+            }
+        };
+        let keys = document_keys(&document);
+        if keys.is_empty() {
+            continue;
+        }
+        let Some(snapshot_id) = capture_observation(&metadata, state).await
+        else {
+            continue;
+        };
+        let snapshot = match sources::load_snapshot(state, &snapshot_id).await {
+            Ok(snapshot) => snapshot,
+            Err(error) => {
+                tracing::warn!(%error, instance_id = metadata.instance.id, %snapshot_id,
+					"Could not load game-setting locale snapshot");
+                continue;
+            }
+        };
+        tracing::info!(instance_id = metadata.instance.id, %snapshot_id, game_version = snapshot.game_version,
+			mods = snapshot.mods.len(),
+			"Game setting locales: snapshot loaded");
+        resolver
+            .index_snapshot(state, &snapshot_id, snapshot.clone())
+            .await?;
+        let mut tx = state.pool.begin().await?;
+        for (id, key) in &keys {
+            let observation = Observation {
+                snapshot: snapshot_id.clone(),
+                raw_key: key.clone(),
+            };
+            storage::observe(
+                &mut tx,
+                &metadata.instance.id,
+                id,
+                &metadata.instance.id,
+                &snapshot.game_version,
+                &observation,
+            )
+            .await?;
+        }
+        tx.commit().await?;
+        tracing::info!(
+            instance_id = metadata.instance.id,
+            options = keys.len(),
+            "Game setting locales: observations recorded"
+        );
+        candidates.push(Candidate {
+            snapshot_id,
+            snapshot,
+            keys,
+        });
+    }
+    let rows = storage::load(&state.pool, None).await?;
+    tracing::info!(
+        candidates = candidates.len(),
+        rows = rows.len(),
+        resolved = rows.iter().filter(|row| row.origin.is_some()).count(),
+        "Game setting locales: resolving translation origins"
+    );
+    let mut pinned = 0;
+    let mut unresolved = 0;
+    for row in rows {
+        if row.origin.is_some() {
+            continue;
+        }
+        let mut observations = Vec::new();
+        if let Some(observation) = &row.observation {
+            observations.push(observation.clone());
+        } else {
+            let mut matching: Vec<_> = candidates
+                .iter()
+                .filter(|c| {
+                    (row.scope.is_empty()
+                        || row.scope == c.snapshot.instance_id)
+                        && c.keys.contains_key(&row.option_id)
+                        && (row.backfilled
+                            || row
+                                .source_instance_id
+                                .as_ref()
+                                .is_none_or(|id| *id == c.snapshot.instance_id)
+                                && row.source_game_version.as_ref().is_none_or(
+                                    |v| *v == c.snapshot.game_version,
+                                ))
+                })
+                .collect();
+            matching.sort_by_key(|c| {
+                (
+                    row.source_instance_id.as_deref()
+                        != Some(c.snapshot.instance_id.as_str()),
+                    row.source_game_version.as_deref()
+                        != Some(c.snapshot.game_version.as_str()),
+                    c.snapshot.instance_id.clone(),
+                )
+            });
+            observations.extend(matching.into_iter().map(|c| Observation {
+                snapshot: c.snapshot_id.clone(),
+                raw_key: c.keys[&row.option_id].clone(),
+            }));
+        }
+        let mut resolved = false;
+        let observation_count = observations.len();
+        for observation in observations {
+            match resolver.resolve(state, &observation).await {
+                Ok(Some(origin)) => {
+                    storage::pin(&state.pool, &row, &origin).await?;
+                    resolved = true;
+                    pinned += 1;
+                    break;
+                }
+                Ok(None) => {}
+                Err(error) => {
+                    tracing::warn!(%error, scope = row.scope, option_id = row.option_id,
+					snapshot_id = observation.snapshot, "Game setting locales: origin resolution failed")
+                }
+            }
+        }
+        if !resolved {
+            tracing::debug!(
+                scope = row.scope,
+                option_id = row.option_id,
+                observation_count,
+                backfilled = row.backfilled,
+                "Game setting locales: no matching translation origin"
+            );
+            unresolved += 1;
+        }
+    }
+    tracing::info!(
+        pinned,
+        unresolved,
+        "Game setting locales: origin resolution finished"
+    );
+    Ok(())
+}
+
+fn is_plain_label(value: &str) -> bool {
+    !value.trim().is_empty() && !value.contains('%') && !value.contains('§')
+}
+
+fn plain_label(value: &str) -> Option<String> {
+    is_plain_label(value).then(|| value.to_owned())
+}
+
+fn minecraft_locale(locale: &str) -> String {
+    match locale {
+        "es-419" => "es_mx".to_owned(),
+        "fil-PH" => "tl_ph".to_owned(),
+        "ms-MY" => "ms_my".to_owned(),
+        "zh-Hans" => "zh_cn".to_owned(),
+        "zh-Hant" => "zh_tw".to_owned(),
+        _ => locale.replace('-', "_").to_ascii_lowercase(),
+    }
+}
+
+/// Loads translations for the settings shown in the modal.
+#[tracing::instrument(skip_all, fields(instance_id, locale, requested = option_ids.len(), refresh_sources), err)]
+pub async fn get_game_setting_locale_labels(
+    instance_id: Option<&str>,
+    locale: &str,
+    option_ids: Vec<String>,
+    refresh_sources: bool,
+) -> crate::Result<GameSettingLocaleLabels> {
+    tracing::info!("Game setting locales: label request received");
+    if option_ids.len() > 16_384 {
+        return Err(input_error("Too many requested game-setting labels"));
+    }
+    let requested: std::collections::HashSet<_> = option_ids
+        .into_iter()
+        .filter(|id| {
+            id.strip_prefix("external:")
+                .and_then(mod_translation_key)
+                .is_some()
+        })
+        .collect();
+    if requested.is_empty() {
+        return Ok(GameSettingLocaleLabels::default());
+    }
+    let locale = minecraft_locale(locale);
+    if !archive::valid_locale(&locale) {
+        return Err(input_error("Invalid Minecraft locale"));
+    }
+    let state = State::get().await?;
+    if refresh_sources {
+        queue_game_locale_index();
+    }
+    let scope = instance_id.unwrap_or("");
+    let mut rows = storage::load(&state.pool, Some(scope)).await?;
+    tracing::info!(
+        scope,
+        rows = rows.len(),
+        resolved = rows.iter().filter(|row| row.origin.is_some()).count(),
+        "Game setting locales: scoped origins loaded"
+    );
+    if scope.is_empty() {
+        let mut sourced: std::collections::HashSet<_> =
+            rows.iter().map(|row| row.option_id.clone()).collect();
+        // Unsaved global options have no provenance row; use an indexed local label until saved.
+        for row in storage::load(&state.pool, None).await? {
+            if !row.scope.is_empty()
+                && requested.contains(&row.option_id)
+                && row.origin.is_some()
+                && sourced.insert(row.option_id.clone())
+            {
+                rows.push(row);
+            }
+        }
+    }
+    tracing::info!(
+        rows = rows.len(),
+        resolved = rows.iter().filter(|row| row.origin.is_some()).count(),
+        "Game setting locales: origins selected including fallbacks"
+    );
+    let hashes: std::collections::HashSet<_> = rows
+        .iter()
+        .filter(|row| requested.contains(&row.option_id))
+        .filter_map(|row| row.origin.as_ref())
+        .filter(|origin| {
+            origin.legacy_game_jar_hash.as_deref()
+                != Some(origin.archive.hash.as_str())
+        })
+        .map(|origin| origin.archive.hash.as_str())
+        .collect();
+    let projects = sources::mod_projects(&state, &hashes.into_iter().collect::<Vec<_>>()).await
+		.unwrap_or_else(|error| {
+			tracing::warn!(%error, "Game setting locales: mod project metadata unavailable");
+			HashMap::new()
+		});
+    let mut result = GameSettingLocaleLabels::default();
+    let mut archives = HashMap::new();
+    let mut dictionaries: HashMap<String, Translations> = HashMap::new();
+    let mut missing_origins = Vec::new();
+    for row in rows {
+        if !requested.contains(&row.option_id) {
+            continue;
+        }
+        let Some(origin) = row.origin else {
+            missing_origins.push(row.option_id);
+            continue;
+        };
+        if origin.legacy_game_jar_hash.as_deref()
+            == Some(origin.archive.hash.as_str())
+        {
+            continue;
+        }
+        let dictionary_id =
+            format!("{}:{}", origin.archive.hash, origin.nested_path);
+        if !dictionaries.contains_key(&dictionary_id) {
+            let index = match cached_archive(
+                &state,
+                &origin.archive,
+                &mut archives,
+            )
+            .await
+            {
+                Ok(index) => index,
+                Err(error) => {
+                    tracing::warn!(%error, option_id = row.option_id, hash = origin.archive.hash,
+						"Game setting locales: label archive unavailable");
+                    continue;
+                }
+            };
+            let Some(bundle) = index
+                .bundles
+                .iter()
+                .find(|b| b.nested_path == origin.nested_path)
+            else {
+                tracing::warn!(
+                    option_id = row.option_id,
+                    nested_path = origin.nested_path,
+                    "Game setting locales: source bundle missing"
+                );
+                continue;
+            };
+            let mut translations =
+                bundle.locales.get("en_us").cloned().unwrap_or_default();
+            if let Some(selected) = bundle.locales.get(&locale) {
+                translations.extend(selected.clone());
+            }
+            bundle.deprecated.apply(&mut translations);
+            tracing::info!(%dictionary_id, %locale, translations = translations.len(),
+				"Game setting locales: dictionary loaded");
+            dictionaries.insert(dictionary_id.clone(), translations);
+        }
+        let translations = &dictionaries[&dictionary_id];
+        let label = translations
+            .get(&origin.translation_key)
+            .and_then(|s| plain_label(s));
+        if let Some(label) = label {
+            let choices = origin
+                .choices
+                .iter()
+                .filter_map(|(value, key)| {
+                    translations
+                        .get(key)
+                        .and_then(|s| plain_label(s))
+                        .map(|label| (value.clone(), label))
+                })
+                .collect();
+            let source = origin
+                .archive
+                .path
+                .file_name()
+                .and_then(|name| name.to_str())
+                .map(|file_name| GameSettingSource {
+                    instance_id: origin.instance_id.clone(),
+                    file_name: file_name.to_owned(),
+                    file_path: format!("mods/{file_name}"),
+                    project: projects.get(&origin.archive.hash).map(
+                        |project| GameSettingSourceProject {
+                            id: project.id.clone(),
+                            title: project.title.clone(),
+                            icon_url: project.icon_url.clone(),
+                        },
+                    ),
+                });
+            result.settings.insert(
+                row.option_id,
+                GameSettingLocaleLabel {
+                    label,
+                    choices,
+                    source,
+                },
+            );
+        } else {
+            tracing::warn!(
+                option_id = row.option_id,
+                key = origin.translation_key,
+                key_present =
+                    translations.contains_key(&origin.translation_key),
+                "Game setting locales: translation missing or rejected as a label"
+            );
+        }
+    }
+    let mut missing: Vec<_> = requested
+        .iter()
+        .filter(|id| !result.settings.contains_key(*id))
+        .collect();
+    missing.sort();
+    tracing::info!(
+        returned = result.settings.len(),
+        ?missing,
+        ?missing_origins,
+        "Game setting locales: label request completed"
+    );
+    Ok(result)
+}
@@ -0,0 +1,144 @@
+use super::sources::{self, ArchiveSource, Snapshot};
+use super::{Observation, Origin, is_plain_label, mod_translation_key};
+use crate::state::State;
+use crate::util::io;
+use std::collections::{BTreeMap, HashMap};
+use std::sync::Arc;
+
+type ArchiveKeys = BTreeMap<String, Arc<str>>;
+
+struct SnapshotIndex {
+    snapshot: Snapshot,
+    keys: BTreeMap<String, (usize, Arc<str>)>,
+}
+
+#[derive(Default)]
+pub(super) struct OriginResolver {
+    archives: HashMap<String, Arc<ArchiveKeys>>,
+    snapshots: HashMap<String, SnapshotIndex>,
+}
+
+impl OriginResolver {
+    pub(super) async fn index_snapshot(
+        &mut self,
+        state: &State,
+        id: &str,
+        snapshot: Snapshot,
+    ) -> crate::Result<()> {
+        if self.snapshots.contains_key(id) {
+            return Ok(());
+        }
+        let mut archives = Vec::new();
+        for (source_index, source) in snapshot.mods.iter().enumerate() {
+            let archive = if let Some(keys) = self.archives.get(&source.hash) {
+                Arc::clone(keys)
+            } else {
+                match load_archive_keys(state, source).await {
+                    Ok(keys) => {
+                        let keys = Arc::new(keys);
+                        self.archives
+                            .insert(source.hash.clone(), Arc::clone(&keys));
+                        keys
+                    }
+                    Err(error) => {
+                        tracing::warn!(hash = source.hash, %error,
+							"Game setting locales: origin archive unavailable");
+                        continue;
+                    }
+                }
+            };
+            archives.push((source_index, archive));
+        }
+        let index = tokio::task::spawn_blocking(move || {
+            let mut keys = BTreeMap::new();
+            for (source_index, archive) in archives {
+                for (key, nested_path) in archive.iter() {
+                    keys.entry(key.clone()).or_insert_with(|| {
+                        (source_index, Arc::clone(nested_path))
+                    });
+                }
+            }
+            SnapshotIndex { snapshot, keys }
+        })
+        .await
+        .map_err(|error| super::input_error(error.to_string()))?;
+        self.snapshots.insert(id.to_owned(), index);
+        Ok(())
+    }
+
+    pub(super) async fn resolve(
+        &mut self,
+        state: &State,
+        observation: &Observation,
+    ) -> crate::Result<Option<Origin>> {
+        let Some(key) = mod_translation_key(&observation.raw_key) else {
+            return Ok(None);
+        };
+        if !self.snapshots.contains_key(&observation.snapshot) {
+            let snapshot =
+                sources::load_snapshot(state, &observation.snapshot).await?;
+            self.index_snapshot(state, &observation.snapshot, snapshot)
+                .await?;
+        }
+        let index = &self.snapshots[&observation.snapshot];
+        Ok(index
+            .keys
+            .get(key)
+            .map(|(source_index, nested_path)| Origin {
+                instance_id: index.snapshot.instance_id.clone(),
+                game_version: index.snapshot.game_version.clone(),
+                legacy_game_jar_hash: None,
+                archive: index.snapshot.mods[*source_index].clone(),
+                nested_path: nested_path.to_string(),
+                translation_key: key.to_owned(),
+                choices: BTreeMap::new(),
+            }))
+    }
+}
+
+/// A complete key index also caches misses until the archive hash changes.
+async fn load_archive_keys(
+    state: &State,
+    source: &ArchiveSource,
+) -> crate::Result<ArchiveKeys> {
+    if !super::archive::valid_hash(&source.hash) {
+        return Err(super::input_error("Invalid locale archive hash"));
+    }
+    let path = sources::root(state)
+        .join("origin-keys-v1")
+        .join(format!("{}.json", source.hash));
+    if let Ok(bytes) = io::read(&path).await {
+        let cached = tokio::task::spawn_blocking(move || {
+            serde_json::from_slice::<ArchiveKeys>(&bytes)
+        })
+        .await
+        .map_err(|error| super::input_error(error.to_string()))?;
+        if let Ok(keys) = cached {
+            return Ok(keys);
+        }
+    }
+    let index = sources::archive_index(state, source).await?;
+    let keys = tokio::task::spawn_blocking(move || {
+        let mut keys = ArchiveKeys::new();
+        for mut bundle in index.bundles {
+            let Some(mut english) = bundle.locales.remove("en_us") else {
+                continue;
+            };
+            bundle.deprecated.apply(&mut english);
+            let nested_path: Arc<str> = bundle.nested_path.into();
+            for (key, value) in english {
+                if is_plain_label(&value) {
+                    keys.entry(key).or_insert_with(|| Arc::clone(&nested_path));
+                }
+            }
+        }
+        keys
+    })
+    .await
+    .map_err(|error| super::input_error(error.to_string()))?;
+    if let Err(error) = sources::write_json(&path, &keys).await {
+        tracing::warn!(hash = source.hash, %error,
+			"Game setting locales: could not cache origin keys");
+    }
+    Ok(keys)
+}
@@ -0,0 +1,207 @@
+use super::super::options_file::{input_error, sha1_bytes};
+use super::archive::{self, ArchiveIndex};
+use crate::state::ModrinthProjectId;
+use crate::state::{CachedEntry, InstanceMetadata, Project, State};
+use crate::util::{fetch, io};
+use serde::{Deserialize, Serialize};
+use std::collections::{BTreeMap, HashMap};
+use std::path::PathBuf;
+
+#[derive(Clone, Serialize, Deserialize)]
+pub(super) struct ArchiveSource {
+    pub hash: String,
+    pub path: PathBuf,
+}
+
+#[derive(Clone, Serialize, Deserialize)]
+pub(super) struct Snapshot {
+    pub instance_id: String,
+    pub game_version: String,
+    pub mods: Vec<ArchiveSource>,
+}
+
+pub(super) async fn mod_projects(
+    state: &State,
+    hashes: &[&str],
+) -> crate::Result<HashMap<String, Project>> {
+    let files = CachedEntry::get_file_many(
+        hashes,
+        None,
+        &state.pool,
+        &state.api_semaphore,
+    )
+    .await?;
+    let project_ids: std::collections::HashSet<_> = files
+        .iter()
+        .filter_map(|file| {
+            ModrinthProjectId::new(file.project_id.as_str().to_string()).ok()
+        })
+        .collect();
+    let projects = CachedEntry::get_project_many(
+        &project_ids.into_iter().collect::<Vec<_>>(),
+        None,
+        &state.pool,
+        &state.api_semaphore,
+    )
+    .await?;
+    let projects: HashMap<_, _> = projects
+        .into_iter()
+        .map(|project| (project.id.clone(), project))
+        .collect();
+    Ok(files
+        .into_iter()
+        .filter_map(|file| {
+            projects
+                .get(&file.project_id)
+                .cloned()
+                .map(|project| (file.hash, project))
+        })
+        .collect())
+}
+
+pub(super) fn root(state: &State) -> PathBuf {
+    state
+        .directories
+        .metadata_dir()
+        .join("game-locales")
+        .join("v1")
+}
+
+pub(super) async fn write_json<T: Serialize>(
+    path: &std::path::Path,
+    data: &T,
+) -> crate::Result<()> {
+    let parent = path
+        .parent()
+        .ok_or_else(|| input_error("Missing locale cache directory"))?;
+    io::create_dir_all(parent).await?;
+    io::write(path, serde_json::to_vec(data)?).await?;
+    Ok(())
+}
+
+pub(super) async fn snapshot_instance(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<String> {
+    let version = &metadata.applied_content_set.game_version;
+    let instance_dir =
+        crate::state::instances::commands::instance_content_root(
+            &state.directories,
+            &metadata.instance,
+        )?;
+    let direct_linked = metadata.instance.is_direct_linked();
+    let cache_key_path = if direct_linked {
+        instance_dir.to_string_lossy().into_owned()
+    } else {
+        metadata.instance.path.clone()
+    };
+    let scanned =
+        crate::state::instances::adapters::filesystem::scan_content_files_from(
+            &instance_dir,
+            &cache_key_path,
+        )?;
+    let scanned: Vec<_> = scanned
+        .into_iter()
+        .filter(|f| f.enabled && f.relative_path.starts_with("mods/"))
+        .collect();
+    let keys: Vec<_> =
+        scanned.iter().map(|f| f.hash_cache_key.as_str()).collect();
+    let hashes = CachedEntry::get_file_hash_many(
+        &keys,
+        None,
+        &state.pool,
+        &state.api_semaphore,
+    )
+    .await?;
+    let by_path: BTreeMap<_, _> =
+        hashes.into_iter().map(|h| (h.path, h.hash)).collect();
+    let mut mods = Vec::new();
+    for file in scanned {
+        let path = instance_dir.join(&file.relative_path);
+        let key = format!("{cache_key_path}/{}", file.relative_path);
+        let hash = match by_path.get(&key) {
+            Some(hash) => hash.clone(),
+            None => fetch::sha1_file_async(&path).await?.1,
+        };
+        mods.push(ArchiveSource { hash, path });
+    }
+    mods.sort_by(|a, b| a.path.cmp(&b.path));
+    let snapshot = Snapshot {
+        instance_id: metadata.instance.id.clone(),
+        game_version: version.clone(),
+        mods,
+    };
+    let bytes = serde_json::to_vec(&snapshot)?;
+    let id = sha1_bytes(&bytes);
+    let path = root(state).join("snapshots").join(format!("{id}.json"));
+    if !io::read(&path).await.is_ok_and(|cached| cached == bytes) {
+        tracing::info!(
+            snapshot_id = id,
+            instance_id = metadata.instance.id,
+            "Game setting locales: writing missing or invalid snapshot cache"
+        );
+        write_json(&path, &snapshot).await?;
+    }
+    Ok(id)
+}
+
+#[tracing::instrument(skip_all, fields(snapshot_id = id), err)]
+pub(super) async fn load_snapshot(
+    state: &State,
+    id: &str,
+) -> crate::Result<Snapshot> {
+    if !archive::valid_hash(id) {
+        return Err(input_error("Invalid locale snapshot hash"));
+    }
+    let bytes =
+        io::read(root(state).join("snapshots").join(format!("{id}.json")))
+            .await?;
+    archive::checked_bytes(bytes.clone(), id).inspect_err(|error| {
+		tracing::warn!(%error, expected_hash = id, actual_hash = sha1_bytes(&bytes),
+			"Game setting locales: snapshot checksum mismatch");
+	})?;
+    Ok(serde_json::from_slice(&bytes)?)
+}
+
+pub(super) async fn archive_index(
+    state: &State,
+    source: &ArchiveSource,
+) -> crate::Result<ArchiveIndex> {
+    if !archive::valid_hash(&source.hash) {
+        return Err(input_error("Invalid locale archive hash"));
+    }
+    let path = root(state)
+        .join("archives")
+        .join(format!("{}.json", source.hash));
+    if let Ok(bytes) = io::read(&path).await {
+        let source_path = source.path.clone();
+        let cached = tokio::task::spawn_blocking(move || {
+            serde_json::from_slice::<ArchiveIndex>(&bytes)
+                .ok()
+                .filter(|index| index.version >= 2 || !source_path.exists())
+        })
+        .await
+        .map_err(|error| input_error(error.to_string()))?;
+        if let Some(index) = cached {
+            tracing::debug!(
+                hash = source.hash,
+                version = index.version,
+                bundles = index.bundles.len(),
+                "Game setting locales: archive cache hit"
+            );
+            return Ok(index);
+        }
+    }
+    tracing::info!(
+        hash = source.hash,
+        "Game setting locales: rebuilding archive cache"
+    );
+    let source = source.clone();
+    let index = tokio::task::spawn_blocking(move || {
+        archive::inspect(&source.path, &source.hash)
+    })
+    .await
+    .map_err(|e| input_error(e.to_string()))??;
+    write_json(&path, &index).await?;
+    Ok(index)
+}
@@ -0,0 +1,132 @@
+use super::{Observation, Origin};
+use sqlx::{Sqlite, SqlitePool, Transaction};
+
+pub(super) struct OriginRow {
+    pub scope: String,
+    pub option_id: String,
+    pub source_instance_id: Option<String>,
+    pub source_game_version: Option<String>,
+    pub backfilled: bool,
+    pub observation: Option<Observation>,
+    pub origin: Option<Origin>,
+}
+
+#[tracing::instrument(skip_all, fields(scope), err)]
+pub(super) async fn load(
+    pool: &SqlitePool,
+    scope: Option<&str>,
+) -> crate::Result<Vec<OriginRow>> {
+    let rows = sqlx::query(
+        "SELECT scope, option_id, source_instance_id, source_game_version,
+        backfilled, observation_json, origin_json
+        FROM game_option_locale_origins
+        WHERE (? IS NULL OR scope = ?)
+        ORDER BY scope, option_id",
+    )
+    .bind(scope)
+    .bind(scope)
+    .fetch_all(pool)
+    .await?;
+    use sqlx::Row;
+    rows.into_iter()
+        .filter(|row| {
+            let option_id: String = row.get("option_id");
+            option_id
+                .strip_prefix("external:")
+                .and_then(super::mod_translation_key)
+                .is_some()
+        })
+        .map(|row| {
+            let scope: String = row.get("scope");
+            let option_id: String = row.get("option_id");
+            let source_instance_id: Option<String> = row.get("source_instance_id");
+            let source_game_version: Option<String> = row.get("source_game_version");
+            let backfilled: bool = row.get("backfilled");
+            let observation_json: Option<String> = row.get("observation_json");
+            let origin_json: Option<String> = row.get("origin_json");
+            let observation = observation_json
+                .as_deref()
+                .map(serde_json::from_str)
+                .transpose()
+                .inspect_err(|error| tracing::warn!(%error, scope = scope, option_id = option_id,
+                    "Game setting locales: stored observation could not be decoded"))?;
+            let origin = origin_json
+                .as_deref()
+                .map(serde_json::from_str)
+                .transpose()
+                .inspect_err(|error| tracing::warn!(%error, scope = scope, option_id = option_id,
+                    "Game setting locales: stored origin could not be decoded"))?;
+            Ok(OriginRow {
+                scope,
+                option_id,
+                source_instance_id,
+                source_game_version,
+                backfilled,
+                observation,
+                origin,
+            })
+        })
+        .collect()
+}
+
+#[tracing::instrument(
+    skip_all,
+    fields(scope, option_id, instance_id, game_version),
+    err
+)]
+pub(super) async fn observe(
+    tx: &mut Transaction<'_, Sqlite>,
+    scope: &str,
+    option_id: &str,
+    instance_id: &str,
+    game_version: &str,
+    observation: &Observation,
+) -> crate::Result<()> {
+    let json = serde_json::to_string(observation)?;
+    sqlx::query(
+        "INSERT INTO game_option_locale_origins
+        (scope, option_id, source_instance_id, source_game_version, observation_json)
+        SELECT ?, ?, ?, ?, ?
+        WHERE ? <> '' OR EXISTS (SELECT 1 FROM synced_game_option_values WHERE option_id = ?)
+        ON CONFLICT(scope, option_id) DO UPDATE SET observation_json = excluded.observation_json
+        WHERE game_option_locale_origins.observation_json IS NULL
+        AND game_option_locale_origins.origin_json IS NULL
+        AND game_option_locale_origins.backfilled = 0
+        AND game_option_locale_origins.source_instance_id = excluded.source_instance_id
+        AND game_option_locale_origins.source_game_version = excluded.source_game_version",
+    )
+    .bind(scope)
+    .bind(option_id)
+    .bind(instance_id)
+    .bind(game_version)
+    .bind(json)
+    .bind(scope)
+    .bind(option_id)
+    .execute(&mut **tx)
+    .await?;
+    Ok(())
+}
+
+#[tracing::instrument(skip_all, fields(scope = row.scope, option_id = row.option_id), err)]
+pub(super) async fn pin(
+    pool: &SqlitePool,
+    row: &OriginRow,
+    origin: &Origin,
+) -> crate::Result<()> {
+    let json = serde_json::to_string(origin)?;
+    let result = sqlx::query(
+        "UPDATE game_option_locale_origins SET origin_json = ?
+        WHERE scope = ? AND option_id = ? AND origin_json IS NULL",
+    )
+    .bind(json)
+    .bind(&row.scope)
+    .bind(&row.option_id)
+    .execute(pool)
+    .await?;
+    tracing::debug!(
+        rows_affected = result.rows_affected(),
+        key = origin.translation_key,
+        "Game setting locales: origin pin completed"
+    );
+    Ok(())
+}
@@ -0,0 +1,73 @@
+//! Syncs selected values from Minecraft's `options.txt` between instances.
+//!
+//! When sync is first enabled, the user chooses an instance to supply the initial
+//! values. Each instance keeps its own `options.txt`; we update only the selected
+//! settings and leave modpack defaults, comments, and disabled settings alone.
+//!
+//! The watcher imports enabled values whenever `options.txt` changes. After the
+//! app writes the file, it stores the file hash and ignores the matching watcher
+//! event. On conflict, the latest save is persisted.
+//!
+//! Minecraft has renamed and reformatted settings over time. `catalog`
+//! contains the file keys and conversions for the versions we support. Any other
+//! key is treated as a custom setting and copied as-is to every synced instance.
+//! Custom settings can be turned off individually in the settings screen.
+
+mod api_types;
+mod catalog;
+mod fullscreen;
+mod instance_support;
+mod launch_overrides;
+pub(crate) mod locales;
+mod options_file;
+mod pack_updates;
+mod read_instance_changes;
+mod settings_editor;
+mod source_selection;
+mod write_shared_settings;
+
+pub use crate::state::{CanonicalValue, GameOptionKind};
+pub use api_types::{
+    EditableGameSetting, GameOptionCompatibility,
+    GameOptionCompatibilityBucket, GameOptionCompatibilityReason,
+    GameOptionCompatibilityStatus, GameOptionEditorChoice,
+    GameOptionEditorDefinition, GameOptionMappingKind,
+    GameOptionValidationIssue, GameOptionValueState,
+    GameOptionsSourceCandidate, GameOptionsSourceIssue, GameSettingCategory,
+    GameSettingChange, GameSettingsEditorState, SaveGameSettingsResult,
+    UpdateGameSettingsRequest,
+};
+pub use launch_overrides::{apply_launcher_overrides, sync_before_launch};
+pub(crate) use locales::{
+    GameLocaleIndexer, queue_game_locale_index, start_game_locale_indexer,
+};
+pub use locales::{GameSettingLocaleLabels, get_game_setting_locale_labels};
+pub use pack_updates::{GameOptionsPackSource, capture_pack_base};
+pub use settings_editor::{get_config, preview_changes, save_changes};
+pub use source_selection::list_sync_sources;
+
+pub(crate) use fullscreen::{
+    shared_fullscreen_value, update_shared_fullscreen_from_app,
+};
+pub(crate) use write_shared_settings::sync_all_participating_instances;
+
+pub(in crate::api::instance) use pack_updates::{
+    detach_instance, prepare_instance_update_with_state,
+};
+pub(in crate::api::instance) use source_selection::initialize_from_source_instance;
+pub(in crate::api::instance) use write_shared_settings::{
+    apply_instance_with_state, capture_instance_file_change,
+};
+
+pub(in crate::api::instance) async fn canonical_exists(
+    state: &crate::state::State,
+) -> crate::Result<bool> {
+    crate::state::shared_game_options_exist(&state.pool).await
+}
+
+const OPTIONS_FILE: &str = "options.txt";
+const CATALOG_REVISION: u32 = 6;
+const MAX_OPTIONS_BYTES: usize = 2 * 1024 * 1024;
+const MAX_OPTIONS_LINES: usize = 16_384;
+const MAX_KEY_BYTES: usize = 1_024;
+const MAX_VALUE_BYTES: usize = 32 * 1024;
@@ -0,0 +1,360 @@
+//! Reads and edits `options.txt` without changing unrelated lines or file formatting.
+
+use super::catalog::{LEGACY_DATA_VERSIONS, release_version};
+use super::{
+    MAX_KEY_BYTES, MAX_OPTIONS_BYTES, MAX_OPTIONS_LINES, MAX_VALUE_BYTES,
+    OPTIONS_FILE,
+};
+use crate::ErrorKind;
+use crate::state::{InstanceMetadata, State};
+use crate::util::io;
+use encoding_rs::{Encoding, UTF_8, UTF_16BE, UTF_16LE};
+use sha1_smol::Sha1;
+use std::collections::HashMap;
+use std::path::{Path, PathBuf};
+
+#[derive(Clone)]
+pub(super) struct GameOptionsDocument {
+    pub(super) encoding: &'static Encoding,
+    pub(super) bom: Bom,
+    pub(super) default_line_ending: String,
+    pub(super) lines: Vec<GameOptionsLine>,
+}
+
+#[derive(Clone, Copy)]
+pub(super) enum Bom {
+    None,
+    Utf8,
+    Utf16Le,
+    Utf16Be,
+}
+
+#[derive(Clone)]
+pub(super) struct GameOptionsLine {
+    pub(super) raw: String,
+    pub(super) ending: String,
+    pub(super) entry: Option<GameOptionsEntry>,
+}
+
+#[derive(Clone)]
+pub(super) struct GameOptionsEntry {
+    pub(super) key: String,
+    pub(super) value: String,
+    pub(super) changed: bool,
+}
+
+impl GameOptionsDocument {
+    pub(super) fn empty() -> Self {
+        Self {
+            encoding: UTF_8,
+            bom: Bom::None,
+            default_line_ending: "\n".to_string(),
+            lines: Vec::new(),
+        }
+    }
+
+    /// Creates settings in the target game's format. Modern key bindings need
+    /// its data version so Minecraft does not run legacy migrations on them.
+    /// Unknown versions without embedded metadata wait for Minecraft's own file.
+    pub(super) async fn for_instance(
+        metadata: &InstanceMetadata,
+        state: &State,
+    ) -> crate::Result<Option<Self>> {
+        let content_set = &metadata.applied_content_set;
+        let version = &content_set.game_version;
+        let version_jar = content_set.loader_version.as_ref().map_or_else(
+            || version.clone(),
+            |loader| format!("{version}-{loader}"),
+        );
+        let path = state
+            .directories
+            .version_dir(&version_jar)
+            .join(format!("{version_jar}.jar"));
+        let embedded_version = if path.exists() {
+            crate::launcher::read_game_version_metadata_from_jar(&path)
+                .await?
+                .and_then(|metadata| metadata.world_version)
+        } else {
+            None
+        };
+        let data_version = embedded_version
+            .or_else(|| LEGACY_DATA_VERSIONS.get(version.as_str()).copied());
+        if data_version.is_none()
+            && !release_version(version)
+                .is_some_and(|(major, minor, _)| major == 1 && minor < 10)
+        {
+            return Ok(None);
+        }
+        let mut document = Self::empty();
+        if let Some(data_version) = data_version {
+            document.set("version", &data_version.to_string(), true)?;
+        }
+        Ok(Some(document))
+    }
+
+    pub(super) fn parse(bytes: &[u8]) -> crate::Result<Self> {
+        if bytes.len() > MAX_OPTIONS_BYTES {
+            return Err(input_error("options.txt is too large to sync safely"));
+        }
+
+        let (bom, encoding, contents) =
+            if bytes.starts_with(&[0xEF, 0xBB, 0xBF]) {
+                (Bom::Utf8, UTF_8, &bytes[3..])
+            } else if bytes.starts_with(&[0xFF, 0xFE]) {
+                (Bom::Utf16Le, UTF_16LE, &bytes[2..])
+            } else if bytes.starts_with(&[0xFE, 0xFF]) {
+                (Bom::Utf16Be, UTF_16BE, &bytes[2..])
+            } else {
+                let mut detector = chardetng::EncodingDetector::new();
+                detector.feed(bytes, true);
+                (Bom::None, detector.guess(None, true), bytes)
+            };
+        let (decoded, decode_errors) =
+            encoding.decode_without_bom_handling(contents);
+        if decode_errors {
+            return Err(input_error(
+                "options.txt contains bytes that cannot be decoded losslessly",
+            ));
+        }
+        let roundtrip = encode_without_bom(encoding, &decoded)?;
+        if roundtrip.as_slice() != contents {
+            return Err(input_error(
+                "options.txt encoding cannot be round-tripped safely",
+            ));
+        }
+
+        let mut lines = Vec::new();
+        let mut start = 0;
+        let source: &str = decoded.as_ref();
+        for (index, byte) in source.as_bytes().iter().enumerate() {
+            if *byte != b'\n' {
+                continue;
+            }
+            let raw_end =
+                if index > start && source.as_bytes()[index - 1] == b'\r' {
+                    index - 1
+                } else {
+                    index
+                };
+            let ending = if raw_end == index { "\n" } else { "\r\n" };
+            lines.push(Self::parse_line(&source[start..raw_end], ending));
+            start = index + 1;
+        }
+        if start < source.len() {
+            lines.push(Self::parse_line(&source[start..], ""));
+        }
+        if lines.len() > MAX_OPTIONS_LINES {
+            return Err(input_error(
+                "options.txt has too many lines to sync safely",
+            ));
+        }
+        let default_line_ending = lines
+            .iter()
+            .find(|line| !line.ending.is_empty())
+            .map(|line| line.ending.clone())
+            .unwrap_or_else(|| "\n".to_string());
+        Ok(Self {
+            encoding,
+            bom,
+            default_line_ending,
+            lines,
+        })
+    }
+
+    pub(super) fn parse_line(raw: &str, ending: &str) -> GameOptionsLine {
+        let entry = raw.split_once(':').and_then(|(key, value)| {
+            if key.is_empty()
+                || key.len() > MAX_KEY_BYTES
+                || value.len() > MAX_VALUE_BYTES
+            {
+                None
+            } else {
+                Some(GameOptionsEntry {
+                    key: key.to_string(),
+                    value: value.to_string(),
+                    changed: false,
+                })
+            }
+        });
+        GameOptionsLine {
+            raw: raw.to_string(),
+            ending: ending.to_string(),
+            entry,
+        }
+    }
+
+    pub(super) fn effective_entries(&self) -> HashMap<&str, (usize, usize)> {
+        let mut entries = HashMap::new();
+        for (index, line) in self.lines.iter().enumerate() {
+            if let Some(entry) = &line.entry {
+                entries
+                    .entry(entry.key.as_str())
+                    .and_modify(|value: &mut (usize, usize)| {
+                        value.0 = index;
+                        value.1 += 1;
+                    })
+                    .or_insert((index, 1));
+            }
+        }
+        entries
+    }
+
+    pub(super) fn value(&self, key: &str) -> Option<&str> {
+        let (index, _) = self.effective_entries().get(key).copied()?;
+        self.lines[index]
+            .entry
+            .as_ref()
+            .map(|entry| entry.value.as_str())
+    }
+
+    pub(super) fn set(
+        &mut self,
+        key: &str,
+        value: &str,
+        insert: bool,
+    ) -> crate::Result<bool> {
+        validate_raw_key_value(key, value)?;
+        if let Some((index, _)) = self.effective_entries().get(key).copied() {
+            let entry = self.lines[index].entry.as_mut().expect("entry index");
+            if entry.value == value {
+                return Ok(false);
+            }
+            entry.value = value.to_string();
+            entry.changed = true;
+            return Ok(true);
+        }
+        if !insert {
+            return Ok(false);
+        }
+
+        let ending = if let Some(last) = self.lines.last_mut() {
+            if last.ending.is_empty() {
+                last.ending = self.default_line_ending.clone();
+                String::new()
+            } else {
+                self.default_line_ending.clone()
+            }
+        } else {
+            self.default_line_ending.clone()
+        };
+        self.lines.push(GameOptionsLine {
+            raw: String::new(),
+            ending,
+            entry: Some(GameOptionsEntry {
+                key: key.to_string(),
+                value: value.to_string(),
+                changed: true,
+            }),
+        });
+        Ok(true)
+    }
+
+    pub(super) fn serialize(&self) -> crate::Result<Vec<u8>> {
+        let mut text = String::new();
+        for line in &self.lines {
+            match &line.entry {
+                Some(entry) if entry.changed => {
+                    text.push_str(&entry.key);
+                    text.push(':');
+                    text.push_str(&entry.value);
+                }
+                _ => text.push_str(&line.raw),
+            }
+            text.push_str(&line.ending);
+        }
+        let encoded = encode_without_bom(self.encoding, &text)?;
+        let bom: &[u8] = match self.bom {
+            Bom::None => &[],
+            Bom::Utf8 => &[0xEF, 0xBB, 0xBF],
+            Bom::Utf16Le => &[0xFF, 0xFE],
+            Bom::Utf16Be => &[0xFE, 0xFF],
+        };
+        let mut result = Vec::with_capacity(bom.len() + encoded.len());
+        result.extend_from_slice(bom);
+        result.extend_from_slice(&encoded);
+        Ok(result)
+    }
+}
+
+pub(super) fn encode_without_bom(
+    encoding: &'static Encoding,
+    text: &str,
+) -> crate::Result<Vec<u8>> {
+    if encoding == UTF_16LE || encoding == UTF_16BE {
+        let mut encoded = Vec::with_capacity(text.len().saturating_mul(2));
+        for unit in text.encode_utf16() {
+            let bytes = if encoding == UTF_16LE {
+                unit.to_le_bytes()
+            } else {
+                unit.to_be_bytes()
+            };
+            encoded.extend_from_slice(&bytes);
+        }
+        return Ok(encoded);
+    }
+
+    let (encoded, _, had_errors) = encoding.encode(text);
+    if had_errors {
+        return Err(input_error(
+            "A synced option value cannot be represented in this file's encoding",
+        ));
+    }
+    Ok(encoded.into_owned())
+}
+
+pub(super) fn input_error(message: impl Into<String>) -> crate::Error {
+    ErrorKind::InputError(message.into()).into()
+}
+
+pub(super) fn validate_raw_key_value(
+    key: &str,
+    value: &str,
+) -> crate::Result<()> {
+    if key.is_empty()
+        || key.len() > MAX_KEY_BYTES
+        || key.contains(':')
+        || key.chars().any(char::is_control)
+    {
+        return Err(input_error("Invalid options.txt setting key"));
+    }
+    if value.len() > MAX_VALUE_BYTES
+        || value
+            .chars()
+            .any(|character| character.is_control() && character != '\t')
+    {
+        return Err(input_error("Invalid options.txt setting value"));
+    }
+    Ok(())
+}
+
+pub(super) fn options_path(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<PathBuf> {
+    Ok(crate::state::instances::commands::instance_content_root(
+        &state.directories,
+        &metadata.instance,
+    )?
+    .join(OPTIONS_FILE))
+}
+
+pub(super) fn sha1_bytes(bytes: &[u8]) -> String {
+    Sha1::from(bytes).digest().to_string()
+}
+
+/// Reads an `options.txt` only when it is safe to rewrite.
+///
+/// The parser keeps its text encoding, line endings, comments, and duplicate keys.
+pub(super) async fn read_document(
+    path: &Path,
+) -> crate::Result<(GameOptionsDocument, Vec<u8>)> {
+    let metadata = tokio::fs::symlink_metadata(path)
+        .await
+        .map_err(|error| io::IOError::with_path(error, path))?;
+    if metadata.file_type().is_symlink() {
+        return Err(input_error("Refusing to sync a symlinked options.txt"));
+    }
+    let bytes = io::read(path).await?;
+    let document = GameOptionsDocument::parse(&bytes)?;
+    Ok((document, bytes))
+}
@@ -0,0 +1,302 @@
+//! Keeps game settings intact when a modpack is installed or updated.
+
+use super::MAX_OPTIONS_BYTES;
+use super::options_file::{input_error, options_path, sha1_bytes};
+use super::write_shared_settings::{
+    apply_shared_settings_to_instance, capture_instance_options,
+    sync_is_active_for_instance,
+};
+use crate::state::{InstanceLink, InstanceMetadata, State, SyncedOption};
+use crate::util::io;
+use encoding_rs::{UTF_8, UTF_16BE, UTF_16LE};
+use std::io::ErrorKind;
+use std::path::Path;
+
+const YOSBR_OPTIONS_PATH: &str = "config/yosbr/options.txt";
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum GameOptionsPackSource {
+    ClientOverrides,
+    Overrides,
+    ClientOverridesYosbr,
+    OverridesYosbr,
+}
+
+impl GameOptionsPackSource {
+    fn as_str(self) -> &'static str {
+        match self {
+            Self::ClientOverrides | Self::ClientOverridesYosbr => {
+                "client_overrides"
+            }
+            Self::Overrides | Self::OverridesYosbr => "overrides",
+        }
+    }
+
+    fn is_yosbr(self) -> bool {
+        matches!(self, Self::ClientOverridesYosbr | Self::OverridesYosbr)
+    }
+}
+
+fn detected_encoding_name(bytes: &[u8]) -> String {
+    if bytes.starts_with(&[0xFF, 0xFE]) {
+        return UTF_16LE.name().to_string();
+    }
+    if bytes.starts_with(&[0xFE, 0xFF]) {
+        return UTF_16BE.name().to_string();
+    }
+    if bytes.starts_with(&[0xEF, 0xBB, 0xBF]) {
+        return UTF_8.name().to_string();
+    }
+    let mut detector = chardetng::EncodingDetector::new();
+    detector.feed(bytes, true);
+    detector.guess(None, true).name().to_string()
+}
+
+fn pack_version_id(metadata: &InstanceMetadata) -> Option<&str> {
+    match &metadata.link {
+        InstanceLink::ModrinthModpack { version_id, .. } => Some(version_id),
+        InstanceLink::ServerProjectModpack {
+            content_version_id, ..
+        } => Some(content_version_id),
+        InstanceLink::ImportedModpack { version_id, .. } => {
+            version_id.as_deref()
+        }
+        InstanceLink::SharedInstance { .. } => None,
+        _ => None,
+    }
+}
+
+async fn read_pack_options(
+    path: &Path,
+    name: &str,
+) -> crate::Result<Option<(Vec<u8>, String, String)>> {
+    let metadata = match tokio::fs::symlink_metadata(path).await {
+        Ok(metadata) => metadata,
+        Err(error) if error.kind() == ErrorKind::NotFound => return Ok(None),
+        Err(error) => return Err(io::IOError::with_path(error, path).into()),
+    };
+    if metadata.file_type().is_symlink() {
+        return Err(input_error(format!(
+            "Refusing to capture a symlinked {name}"
+        )));
+    }
+    if metadata.len() > MAX_OPTIONS_BYTES as u64 {
+        return Err(input_error(format!(
+            "The modpack {name} is too large to capture for syncing"
+        )));
+    }
+    let bytes = io::read(path).await?;
+    let sha1 = sha1_bytes(&bytes);
+    let encoding = detected_encoding_name(&bytes);
+    Ok(Some((bytes, sha1, encoding)))
+}
+
+async fn options_target_exists(path: &Path) -> crate::Result<bool> {
+    match tokio::fs::symlink_metadata(path).await {
+        Ok(metadata) if metadata.file_type().is_symlink() => {
+            Err(input_error("Refusing to replace a symlinked options.txt"))
+        }
+        Ok(_) => Ok(true),
+        Err(error) if error.kind() == ErrorKind::NotFound => Ok(false),
+        Err(error) => Err(io::IOError::with_path(error, path).into()),
+    }
+}
+
+pub(super) async fn materialize_yosbr_options_if_missing(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<()> {
+    let path = options_path(metadata, state)?;
+    if options_target_exists(&path).await? {
+        return Ok(());
+    }
+    let template_path =
+        crate::state::instances::commands::instance_content_root(
+            &state.directories,
+            &metadata.instance,
+        )?
+        .join(YOSBR_OPTIONS_PATH);
+    let Some((bytes, _, _)) =
+        read_pack_options(&template_path, "YOSBR options.txt").await?
+    else {
+        return Ok(());
+    };
+    io::write(&path, bytes).await?;
+    Ok(())
+}
+
+pub(in crate::api::instance) async fn detach_instance(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<()> {
+    let feature = SyncedOption::GameOptions.as_str();
+    sqlx::query(
+        "DELETE FROM instance_sync_checkpoints
+        WHERE instance_id = ? AND feature = ?",
+    )
+    .bind(metadata.instance.id)
+    .bind(feature)
+    .execute(&state.pool)
+    .await?;
+    Ok(())
+}
+
+/// Before replacing modpack files, saves `options.txt` and shares any settings the
+/// player changed in Minecraft.
+pub(in crate::api::instance) async fn prepare_instance_update_with_state(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<()> {
+    sqlx::query(
+        "DELETE FROM instance_game_option_update_state WHERE instance_id = ?",
+    )
+    .bind(metadata.instance.id)
+    .execute(&state.pool)
+    .await?;
+    if sync_is_active_for_instance(metadata, state).await? {
+        let _ = capture_instance_options(metadata, state, true).await?;
+    }
+    let path = options_path(metadata, state)?;
+    let (had_file, bytes, sha1) = if path.exists() {
+        let file_metadata = tokio::fs::symlink_metadata(&path)
+            .await
+            .map_err(|error| io::IOError::with_path(error, &path))?;
+        if file_metadata.file_type().is_symlink() {
+            return Err(input_error(
+                "Refusing to prepare a symlinked options.txt for a modpack update",
+            ));
+        }
+        if file_metadata.len() > MAX_OPTIONS_BYTES as u64 {
+            return Err(input_error(
+                "options.txt is too large to preserve for a modpack update",
+            ));
+        }
+        let bytes = io::read(&path).await?;
+        (true, Some(bytes.clone()), Some(sha1_bytes(&bytes)))
+    } else {
+        (false, None, None)
+    };
+    sqlx::query(
+        "INSERT INTO instance_game_option_update_state
+            (instance_id, had_file, sha1, document)
+        VALUES (?, ?, ?, ?)
+        ON CONFLICT(instance_id) DO UPDATE SET
+            had_file = excluded.had_file, sha1 = excluded.sha1,
+            document = excluded.document",
+    )
+    .bind(metadata.instance.id)
+    .bind(had_file)
+    .bind(sha1)
+    .bind(bytes)
+    .execute(&state.pool)
+    .await?;
+    Ok(())
+}
+
+/// Keeps the new modpack's `options.txt` as its default, then reapplies the user's
+/// shared settings.
+pub async fn capture_pack_base(
+    instance_id: &str,
+    source: Option<GameOptionsPackSource>,
+) -> crate::Result<()> {
+    let state = State::get().await?;
+    let _guard = state.lock_synced_options().await;
+    let metadata = crate::state::get_instance(instance_id, &state.pool)
+        .await?
+        .ok_or_else(|| input_error("Unknown instance"))?;
+    let path = options_path(&metadata, &state)?;
+    let feature = SyncedOption::GameOptions.as_str();
+    sqlx::query(
+        "DELETE FROM instance_sync_checkpoints
+        WHERE instance_id = ? AND feature = ?",
+    )
+    .bind(instance_id)
+    .bind(feature)
+    .execute(&state.pool)
+    .await?;
+
+    if source.is_none() {
+        let pending = sqlx::query(
+            "SELECT had_file, document
+            FROM instance_game_option_update_state
+            WHERE instance_id = ?",
+        )
+        .bind(instance_id)
+        .fetch_optional(&state.pool)
+        .await?;
+        if let Some(pending) = pending {
+            use sqlx::Row;
+            let had_file: bool = pending.get("had_file");
+            let document: Option<Vec<u8>> = pending.get("document");
+            if had_file {
+                if let Some(document) = document {
+                    io::write(&path, document).await?;
+                }
+            } else if path.exists() {
+                io::remove_file(&path).await?;
+            }
+        }
+    }
+
+    let captured = if source.is_some_and(GameOptionsPackSource::is_yosbr) {
+        let template_path =
+            crate::state::instances::commands::instance_content_root(
+                &state.directories,
+                &metadata.instance,
+            )?
+            .join(YOSBR_OPTIONS_PATH);
+        let template = read_pack_options(&template_path, "YOSBR options.txt")
+            .await?
+            .ok_or_else(|| {
+                input_error("The modpack YOSBR options.txt is missing")
+            })?;
+        if !options_target_exists(&path).await? {
+            io::write(&path, template.0.clone()).await?;
+        }
+        Some(template)
+    } else {
+        read_pack_options(&path, "options.txt").await?
+    };
+    let (document_bytes, sha1, encoding) = captured
+        .map(|(document, sha1, encoding)| {
+            (Some(document), Some(sha1), Some(encoding))
+        })
+        .unwrap_or((None, None, None));
+    let source_name =
+        source.map(GameOptionsPackSource::as_str).unwrap_or("none");
+    let version_id = pack_version_id(&metadata);
+    sqlx::query(
+        "INSERT INTO instance_game_option_pack_bases
+            (instance_id, pack_version_id, source, sha1, encoding, document)
+        VALUES (?, ?, ?, ?, ?, ?)
+        ON CONFLICT(instance_id) DO UPDATE SET
+            pack_version_id = excluded.pack_version_id,
+            source = excluded.source, sha1 = excluded.sha1,
+            encoding = excluded.encoding, document = excluded.document",
+    )
+    .bind(instance_id)
+    .bind(version_id)
+    .bind(source_name)
+    .bind(sha1)
+    .bind(encoding)
+    .bind(document_bytes)
+    .execute(&state.pool)
+    .await?;
+    sqlx::query(
+        "DELETE FROM instance_game_option_update_state WHERE instance_id = ?",
+    )
+    .bind(instance_id)
+    .execute(&state.pool)
+    .await?;
+
+    if sync_is_active_for_instance(&metadata, &state).await?
+        && let Err(error) =
+            apply_shared_settings_to_instance(&metadata, &state, true).await
+    {
+        tracing::warn!(
+            "Captured the modpack options.txt for {}, but shared settings could not be overlaid yet: {error}",
+            metadata.instance.id
+        );
+    }
+    Ok(())
+}
@@ -0,0 +1,371 @@
+//! Imports saved `options.txt` settings into the canonical values.
+
+use super::CATALOG_REVISION;
+use super::api_types::canonical_values_equal;
+use super::catalog::*;
+use super::fullscreen::update_app_fullscreen_setting;
+use super::launch_overrides::currently_launcher_owned_keys;
+use super::options_file::{GameOptionsDocument, validate_raw_key_value};
+use crate::state::{
+    CanonicalValue, GameOptionKind, InstanceMetadata, State,
+    load_game_option_preferences, load_game_options_sync_state,
+    load_shared_game_options,
+};
+use chrono::Utc;
+use std::collections::HashSet;
+
+pub(super) fn custom_setting_id(key: &str) -> String {
+    format!("external:{key}")
+}
+
+/// Imports every enabled setting present in `options.txt`. The caller skips file
+/// hashes produced by app writes.
+pub(super) async fn read_instance_changes_into_shared_settings(
+    metadata: &InstanceMetadata,
+    document: &GameOptionsDocument,
+    state: &State,
+) -> crate::Result<bool> {
+    let values = load_shared_game_options(&state.pool).await?;
+    let preferences = load_game_option_preferences(&state.pool).await?;
+    let launcher_keys = currently_launcher_owned_keys(metadata);
+    let now = Utc::now().timestamp();
+    let mut updates = Vec::new();
+    for (option_id, stored) in &values {
+        if !preferences
+            .get(option_id)
+            .is_some_and(|preference| preference.enabled)
+        {
+            continue;
+        }
+        if matches!(stored.kind, GameOptionKind::External)
+            && stored.raw_key.is_none()
+        {
+            continue;
+        }
+        if stored
+            .raw_key
+            .as_deref()
+            .is_some_and(|key| setting_by_file_key(key).is_some())
+        {
+            continue;
+        }
+        let definition = setting_by_id(option_id);
+        if definition.is_some()
+            && !supported_settings_cover_game_version(
+                &metadata.applied_content_set.game_version,
+            )
+        {
+            continue;
+        }
+        let current_key = if let Some(definition) = definition {
+            observed_physical_key(
+                definition,
+                document,
+                &metadata.applied_content_set.game_version,
+            )
+        } else {
+            stored.raw_key.clone()
+        };
+        let Some(current_key) = current_key else {
+            continue;
+        };
+        if launcher_keys.contains(&current_key) {
+            continue;
+        }
+        let Some(current_raw) = document.value(&current_key) else {
+            continue;
+        };
+        let candidate = if let Some(definition) = definition {
+            decode_value_for_version(
+                definition,
+                &current_key,
+                current_raw,
+                &metadata.applied_content_set.game_version,
+            )
+        } else if matches!(stored.kind, GameOptionKind::External) {
+            if validate_raw_key_value(&current_key, current_raw).is_err() {
+                continue;
+            }
+            Some(CanonicalValue::ExternalRaw(current_raw.to_string()))
+        } else {
+            None
+        };
+        let Some(candidate) = candidate else {
+            continue;
+        };
+        if stored
+            .value
+            .as_ref()
+            .is_some_and(|current| canonical_values_equal(current, &candidate))
+        {
+            continue;
+        }
+        updates.push((option_id.to_string(), candidate, stored.revision));
+    }
+
+    let mut changed = false;
+    let mut fullscreen_value = None;
+    if !updates.is_empty() {
+        let (canonical_revision, _) =
+            load_game_options_sync_state(&state.pool, CATALOG_REVISION).await?;
+        let mut tx = state.pool.begin().await?;
+        for (option_id, candidate, revision) in updates {
+            let next_revision = revision.saturating_add(1) as i64;
+            let current_revision = revision as i64;
+            let value_json = serde_json::to_string(&candidate)?;
+            let canonical_type = candidate.type_name();
+            let result = sqlx::query(
+                "UPDATE synced_game_option_values
+                SET canonical_type = ?, canonical_value_json = ?, seeded = 1,
+                    revision = ?, origin = 'instance', source_game_version = ?,
+                    source_instance_id = ?, updated_at = ?
+                WHERE option_id = ? AND revision = ?",
+            )
+            .bind(canonical_type)
+            .bind(value_json)
+            .bind(next_revision)
+            .bind(metadata.applied_content_set.game_version)
+            .bind(metadata.instance.id)
+            .bind(now)
+            .bind(option_id)
+            .bind(current_revision)
+            .execute(&mut *tx)
+            .await?;
+            if result.rows_affected() == 0 {
+                continue;
+            }
+            if option_id == "fullscreen" {
+                fullscreen_value = Some(candidate.clone());
+            }
+            changed = true;
+        }
+        if changed {
+            let next_revision = canonical_revision.saturating_add(1) as i64;
+            sqlx::query(
+                "UPDATE synced_game_option_state
+                SET revision = ?, catalog_revision = ?
+                WHERE singleton = 1",
+            )
+            .bind(next_revision)
+            .bind(CATALOG_REVISION as i64)
+            .execute(&mut *tx)
+            .await?;
+        }
+        if let Some(value) = fullscreen_value.as_ref() {
+            update_app_fullscreen_setting(&mut tx, value, true).await?;
+        }
+        tx.commit().await?;
+    }
+    let discovered =
+        discover_custom_settings(metadata, document, &launcher_keys, state)
+            .await?;
+    Ok(discovered || changed)
+}
+
+/// Finds settings added by mods and adds them to the shared settings list.
+pub(super) async fn discover_custom_settings(
+    metadata: &InstanceMetadata,
+    document: &GameOptionsDocument,
+    excluded_keys: &HashSet<String>,
+    state: &State,
+) -> crate::Result<bool> {
+    let existing = load_shared_game_options(&state.pool).await?;
+    let preferences = load_game_option_preferences(&state.pool).await?;
+    let (canonical_revision, _) =
+        load_game_options_sync_state(&state.pool, CATALOG_REVISION).await?;
+    let entries = document.effective_entries();
+    let now = Utc::now().timestamp();
+    let mut discovered = false;
+    let locale_snapshot =
+        if super::locales::has_localizable_mod_settings(document)
+            && document.effective_entries().keys().any(|key| {
+                let id = setting_by_file_key(key)
+                    .map(|s| s.id.to_owned())
+                    .unwrap_or_else(|| custom_setting_id(key));
+                !existing.contains_key(&id)
+            })
+        {
+            super::locales::capture_observation(metadata, state).await
+        } else {
+            None
+        };
+    let mut tx = state.pool.begin().await?;
+    let game_version = metadata.applied_content_set.game_version.as_str();
+
+    for definition in all_supported_settings() {
+        for key in definition.keys {
+            let custom_id = custom_setting_id(key);
+            let Some(custom) = existing.get(&custom_id) else {
+                continue;
+            };
+            if !custom.seeded {
+                continue;
+            }
+            let revision = custom.revision.saturating_add(1) as i64;
+            sqlx::query(
+                "UPDATE synced_game_option_values
+                SET seeded = 0, revision = ?, updated_at = ?
+                WHERE option_id = ?",
+            )
+            .bind(revision)
+            .bind(now)
+            .bind(custom_id)
+            .execute(&mut *tx)
+            .await?;
+            sqlx::query(
+                "UPDATE synced_game_option_preferences
+                SET enabled = 0, source = 'catalog_default', revision = ?
+                WHERE option_id = ?",
+            )
+            .bind(revision)
+            .bind(custom_id)
+            .execute(&mut *tx)
+            .await?;
+            discovered = true;
+        }
+    }
+
+    if supported_settings_cover_game_version(game_version) {
+        for definition in all_supported_settings() {
+            if existing.contains_key(definition.id) {
+                continue;
+            }
+            let discovered_value = definition.keys.iter().find_map(|key| {
+                if excluded_keys.contains(*key) {
+                    return None;
+                }
+                let raw = document.value(key)?;
+                decode_value_for_version(definition, key, raw, game_version)
+            });
+            let Some(value) = discovered_value else {
+                continue;
+            };
+            let value_json = serde_json::to_string(&value)?;
+            let canonical_type = value.type_name();
+            sqlx::query(
+                "INSERT INTO synced_game_option_values
+                    (option_id, kind, raw_key, canonical_type,
+                     canonical_value_json, value_codec, seeded, revision, origin,
+                     source_game_version, source_instance_id, updated_at)
+                VALUES (?, 'vanilla', NULL, ?, ?, 'catalog', 1, 1,
+                    'instance', ?, ?, ?)",
+            )
+            .bind(definition.id)
+            .bind(canonical_type)
+            .bind(value_json)
+            .bind(game_version)
+            .bind(metadata.instance.id)
+            .bind(now)
+            .execute(&mut *tx)
+            .await?;
+            sqlx::query(
+                "INSERT INTO synced_game_option_preferences
+                    (option_id, enabled, source, revision)
+                VALUES (?, ?, 'catalog_default', 1)",
+            )
+            .bind(definition.id)
+            .bind(definition.default_on)
+            .execute(&mut *tx)
+            .await?;
+            discovered = true;
+        }
+    }
+
+    for (key, (index, _)) in entries {
+        if excluded_keys.contains(key)
+            || setting_by_file_key(key).is_some()
+            || is_never_sync_key(key)
+        {
+            continue;
+        }
+        let Some(entry) = &document.lines[index].entry else {
+            continue;
+        };
+        if validate_raw_key_value(key, &entry.value).is_err() {
+            continue;
+        }
+        let option_id = custom_setting_id(key);
+        let should_seed =
+            existing.get(&option_id).is_none_or(|stored| !stored.seeded);
+        if !should_seed {
+            continue;
+        }
+        let revision = existing
+            .get(&option_id)
+            .map(|stored| stored.revision)
+            .unwrap_or(0)
+            .max(
+                preferences
+                    .get(&option_id)
+                    .map(|preference| preference.revision)
+                    .unwrap_or(0),
+            )
+            .saturating_add(1) as i64;
+        let value = CanonicalValue::ExternalRaw(entry.value.clone());
+        let value_json = serde_json::to_string(&value)?;
+
+        sqlx::query(
+            "INSERT INTO synced_game_option_values
+                (option_id, kind, raw_key, canonical_type,
+                 canonical_value_json, value_codec, seeded, revision, origin,
+                 source_game_version, source_instance_id, updated_at)
+            VALUES (?, 'external', ?, 'external_raw', ?, 'exact_raw',
+                1, ?, 'instance', ?, ?, ?)
+            ON CONFLICT(option_id) DO UPDATE SET
+                raw_key = excluded.raw_key,
+                canonical_value_json = excluded.canonical_value_json,
+                seeded = 1, revision = excluded.revision,
+                origin = 'instance',
+                source_game_version = excluded.source_game_version,
+                source_instance_id = excluded.source_instance_id,
+                updated_at = excluded.updated_at",
+        )
+        .bind(option_id)
+        .bind(key)
+        .bind(value_json)
+        .bind(revision)
+        .bind(game_version)
+        .bind(metadata.instance.id)
+        .bind(now)
+        .execute(&mut *tx)
+        .await?;
+        sqlx::query(
+            "
+			INSERT INTO synced_game_option_preferences
+				(option_id, enabled, source, revision)
+            VALUES (?, 0, 'discovery_default', ?)
+			ON CONFLICT(option_id) DO NOTHING
+			",
+        )
+        .bind(&option_id)
+        .bind(revision)
+        .execute(&mut *tx)
+        .await?;
+        discovered = true;
+    }
+
+    if discovered {
+        let next_revision = canonical_revision.saturating_add(1) as i64;
+        sqlx::query(
+            "UPDATE synced_game_option_state
+            SET revision = ?, catalog_revision = ?
+            WHERE singleton = 1",
+        )
+        .bind(next_revision)
+        .bind(CATALOG_REVISION as i64)
+        .execute(&mut *tx)
+        .await?;
+    }
+    super::locales::record_observations(
+        &mut tx,
+        metadata,
+        document,
+        locale_snapshot.as_deref(),
+    )
+    .await;
+    tx.commit().await?;
+    if discovered {
+        super::locales::queue_game_locale_index();
+    }
+    Ok(discovered)
+}
@@ -0,0 +1,522 @@
+//! Loads, previews, and saves the game settings shown in the app.
+
+use super::CATALOG_REVISION;
+use super::api_types::*;
+use super::catalog::*;
+use super::fullscreen::update_app_fullscreen_setting;
+use super::instance_support::{
+    describe_instance_support, find_common_local_value,
+    load_participating_instances, summary_revision,
+};
+use super::options_file::input_error;
+use super::write_shared_settings::sync_all_participating_instances;
+use crate::state::{
+    CanonicalValue, GameOptionKind, State, StoredOption,
+    game_options_sync_is_enabled, load_game_option_preferences,
+    load_game_options_sync_state, load_shared_game_options,
+};
+use chrono::Utc;
+
+fn validation_issue(
+    sync_enabled: bool,
+    value: Option<&CanonicalValue>,
+    compatibility: &GameOptionCompatibility,
+) -> Option<GameOptionValidationIssue> {
+    if !sync_enabled {
+        return None;
+    }
+    if value.is_none() {
+        return Some(GameOptionValidationIssue::MissingValue);
+    }
+    if compatibility.total_participating > 0 && compatibility.will_receive == 0
+    {
+        return Some(GameOptionValidationIssue::NoCompatibleInstances);
+    }
+    None
+}
+
+/// Loads everything shown in the game-settings modal.
+///
+/// It returns message IDs and setting details; the frontend provides the translated
+/// labels and explanations.
+pub(super) async fn load_settings_editor(
+    state: &State,
+) -> crate::Result<GameSettingsEditorState> {
+    let (canonical_revision, catalog_revision) =
+        load_game_options_sync_state(&state.pool, CATALOG_REVISION).await?;
+    let values = load_shared_game_options(&state.pool).await?;
+    let preferences = load_game_option_preferences(&state.pool).await?;
+    let participants = load_participating_instances(state).await?;
+    let mut settings = Vec::new();
+
+    for definition in all_supported_settings() {
+        let retained = values.contains_key(definition.id)
+            || preferences.contains_key(definition.id);
+        let observed = participants.iter().any(|participant| {
+            participant.document.as_ref().is_some_and(|document| {
+                definition
+                    .keys
+                    .iter()
+                    .any(|key| document.value(key).is_some())
+            })
+        });
+        if !retained && !observed {
+            continue;
+        }
+        let stored = values.get(definition.id).cloned().unwrap_or_else(|| {
+            StoredOption {
+                option_id: definition.id.to_string(),
+                kind: GameOptionKind::Vanilla,
+                raw_key: None,
+                value: None,
+                seeded: false,
+                revision: 0,
+            }
+        });
+        let preference = preferences.get(definition.id);
+        let (canonical_value, value_state) = if stored.seeded {
+            (stored.value.clone(), GameOptionValueState::Canonical)
+        } else {
+            find_common_local_value(Some(definition), &stored, &participants)
+        };
+        let compatibility = describe_instance_support(
+            Some(definition),
+            &stored,
+            canonical_value.as_ref(),
+            &participants,
+        );
+        let sync_enabled =
+            preference.map(|value| value.enabled).unwrap_or(false);
+        let validation_error = validation_issue(
+            sync_enabled,
+            canonical_value.as_ref(),
+            &compatibility,
+        );
+        settings.push(EditableGameSetting {
+            option_id: definition.id.to_string(),
+            category_id: definition.category.to_string(),
+            kind: GameOptionKind::Vanilla,
+            raw_key: None,
+            sync_enabled,
+            canonical_value,
+            value_state,
+            option_revision: stored
+                .revision
+                .max(preference.map(|value| value.revision).unwrap_or(0)),
+            editor: editor_for(definition),
+            compatibility,
+            validation_error,
+            controlled: false,
+        });
+    }
+
+    let mut custom_values = values
+        .values()
+        .filter(|value| {
+            matches!(value.kind, GameOptionKind::External)
+                && value
+                    .raw_key
+                    .as_deref()
+                    .is_none_or(|key| setting_by_file_key(key).is_none())
+        })
+        .cloned()
+        .collect::<Vec<_>>();
+    custom_values.sort_by(|left, right| left.raw_key.cmp(&right.raw_key));
+    for stored in custom_values {
+        let preference = preferences.get(&stored.option_id);
+        let (canonical_value, value_state) = if stored.seeded {
+            (stored.value.clone(), GameOptionValueState::Canonical)
+        } else {
+            find_common_local_value(None, &stored, &participants)
+        };
+        let compatibility = describe_instance_support(
+            None,
+            &stored,
+            canonical_value.as_ref(),
+            &participants,
+        );
+        let sync_enabled = preference.is_some_and(|value| value.enabled);
+        let validation_error = validation_issue(
+            sync_enabled,
+            canonical_value.as_ref(),
+            &compatibility,
+        );
+        settings.push(EditableGameSetting {
+            option_id: stored.option_id.clone(),
+            category_id: "custom".to_string(),
+            kind: GameOptionKind::External,
+            raw_key: stored.raw_key.clone(),
+            sync_enabled,
+            canonical_value,
+            value_state,
+            option_revision: stored
+                .revision
+                .max(preference.map(|value| value.revision).unwrap_or(0)),
+            editor: custom_setting_editor(),
+            compatibility,
+            validation_error,
+            controlled: false,
+        });
+    }
+
+    let category_definitions = [
+        "skin_customization",
+        "video",
+        "language",
+        "music_and_sound",
+        "controls",
+        "chat",
+        "accessibility",
+        "online",
+        "custom",
+    ];
+    let categories = category_definitions
+        .into_iter()
+        .filter(|id| {
+            *id == "custom"
+                || settings.iter().any(|setting| setting.category_id == *id)
+        })
+        .map(|id| GameSettingCategory {
+            id: id.to_string(),
+            is_custom: id == "custom",
+        })
+        .collect();
+
+    Ok(GameSettingsEditorState {
+        summary_revision: summary_revision(canonical_revision, &participants),
+        canonical_revision,
+        catalog_revision,
+        total_participating: participants.len() as u32,
+        categories,
+        settings,
+    })
+}
+
+pub async fn get_config() -> crate::Result<GameSettingsEditorState> {
+    let state = State::get().await?;
+    let _guard = state.lock_synced_options().await;
+    load_settings_editor(&state).await
+}
+
+/// Previews how the user's unsaved changes would apply to their instances.
+pub async fn preview_changes(
+    request: UpdateGameSettingsRequest,
+) -> crate::Result<GameSettingsEditorState> {
+    let state = State::get().await?;
+    let _guard = state.lock_synced_options().await;
+    if request.expected_catalog_revision != CATALOG_REVISION {
+        return load_settings_editor(&state).await;
+    }
+    let mut editor_state = load_settings_editor(&state).await?;
+    let participants = load_participating_instances(&state).await?;
+    for change in request.changes {
+        let Some(setting) = editor_state
+            .settings
+            .iter_mut()
+            .find(|setting| setting.option_id == change.option_id)
+        else {
+            continue;
+        };
+        if setting.option_revision != change.base_option_revision {
+            setting.validation_error =
+                Some(GameOptionValidationIssue::ChangedSinceOpened);
+            continue;
+        }
+        if let Some(value) = change.canonical_value {
+            let definition = setting_by_id(&setting.option_id);
+            if let Some(value) = value {
+                if validate_canonical_value(definition, &value).is_err() {
+                    setting.validation_error =
+                        Some(GameOptionValidationIssue::InvalidValue);
+                } else {
+                    setting.canonical_value = Some(value);
+                    setting.value_state = GameOptionValueState::Canonical;
+                    setting.validation_error = None;
+                }
+            } else {
+                setting.canonical_value = None;
+                setting.value_state = GameOptionValueState::Unset;
+                setting.validation_error = None;
+            }
+        }
+        if let Some(enabled) = change.sync_enabled {
+            setting.sync_enabled = enabled;
+        }
+        let stored = StoredOption {
+            option_id: setting.option_id.clone(),
+            kind: setting.kind,
+            raw_key: setting.raw_key.clone(),
+            value: setting.canonical_value.clone(),
+            seeded: setting.canonical_value.is_some(),
+            revision: setting.option_revision,
+        };
+        setting.compatibility = describe_instance_support(
+            setting_by_id(&setting.option_id),
+            &stored,
+            setting.canonical_value.as_ref(),
+            &participants,
+        );
+        if setting.sync_enabled && setting.canonical_value.is_none() {
+            setting.validation_error =
+                Some(GameOptionValidationIssue::MissingValue);
+        } else if setting.sync_enabled
+            && setting.compatibility.total_participating > 0
+            && setting.compatibility.will_receive == 0
+        {
+            setting.validation_error =
+                Some(GameOptionValidationIssue::NoCompatibleInstances);
+        }
+    }
+    Ok(editor_state)
+}
+
+/// Saves changes if nothing has changed since the modal opened, then updates each
+/// instance that can receive them.
+pub async fn save_changes(
+    request: UpdateGameSettingsRequest,
+) -> crate::Result<SaveGameSettingsResult> {
+    let state = State::get().await?;
+    let _guard = state.lock_synced_options().await;
+    if !game_options_sync_is_enabled(&state.pool).await? {
+        return Err(input_error(
+            "Turn on game-settings sync before editing shared values.",
+        ));
+    }
+    let current_editor = load_settings_editor(&state).await?;
+    let UpdateGameSettingsRequest {
+        expected_summary_revision,
+        expected_canonical_revision,
+        expected_catalog_revision,
+        changes,
+    } = request;
+    if expected_catalog_revision != CATALOG_REVISION
+        || expected_summary_revision != current_editor.summary_revision
+        || expected_canonical_revision != current_editor.canonical_revision
+    {
+        return Ok(SaveGameSettingsResult {
+            state: Some(current_editor),
+            conflicts: changes
+                .into_iter()
+                .map(|change| change.option_id)
+                .collect(),
+            ..SaveGameSettingsResult::default()
+        });
+    }
+    let stored_values = load_shared_game_options(&state.pool).await?;
+    let participants = load_participating_instances(&state).await?;
+    let mut conflicts = Vec::new();
+    let mut accepted = Vec::new();
+
+    for mut change in changes {
+        let Some(setting) = current_editor
+            .settings
+            .iter()
+            .find(|setting| setting.option_id == change.option_id)
+        else {
+            return Err(input_error(format!(
+                "Unknown game setting {}",
+                change.option_id
+            )));
+        };
+        if setting.option_revision != change.base_option_revision {
+            conflicts.push(change.option_id);
+            continue;
+        }
+        if let Some(Some(value)) = &change.canonical_value {
+            validate_canonical_value(setting_by_id(&setting.option_id), value)?;
+        }
+        let resulting_enabled =
+            change.sync_enabled.unwrap_or(setting.sync_enabled);
+        let stored_seeded = stored_values
+            .get(&setting.option_id)
+            .is_some_and(|stored| stored.seeded);
+        if resulting_enabled
+            && !stored_seeded
+            && change.canonical_value.is_none()
+            && setting.canonical_value.is_some()
+        {
+            change.canonical_value = Some(setting.canonical_value.clone());
+        }
+        let resulting_value = match &change.canonical_value {
+            Some(value) => value.as_ref(),
+            None => setting.canonical_value.as_ref(),
+        };
+        if resulting_enabled {
+            if resulting_value.is_none() {
+                return Err(input_error(format!(
+                    "Choose a value before enabling {}",
+                    setting.option_id
+                )));
+            }
+            let projected = StoredOption {
+                option_id: setting.option_id.clone(),
+                kind: setting.kind,
+                raw_key: setting.raw_key.clone(),
+                value: resulting_value.cloned(),
+                seeded: resulting_value.is_some(),
+                revision: setting.option_revision,
+            };
+            let compatibility = describe_instance_support(
+                setting_by_id(&setting.option_id),
+                &projected,
+                resulting_value,
+                &participants,
+            );
+            if compatibility.total_participating > 0
+                && compatibility.will_receive == 0
+            {
+                return Err(input_error(format!(
+                    "{} is not compatible with any participating instance",
+                    setting.option_id
+                )));
+            }
+        }
+        accepted.push((setting.clone(), change));
+    }
+
+    let mut changed = false;
+    let mut fullscreen_value = None;
+    let mut tx = state.pool.begin().await?;
+    for (setting, change) in accepted {
+        let resulting_enabled =
+            change.sync_enabled.unwrap_or(setting.sync_enabled);
+        let value_changed =
+            change.canonical_value.as_ref().is_some_and(|value| {
+                setting.value_state != GameOptionValueState::Canonical
+                    || value.as_ref() != setting.canonical_value.as_ref()
+            });
+        let selection_changed = change
+            .sync_enabled
+            .is_some_and(|enabled| enabled != setting.sync_enabled);
+        if !value_changed && !selection_changed {
+            continue;
+        }
+        if resulting_enabled
+            && setting.option_id == "fullscreen"
+            && let Some(value) = change
+                .canonical_value
+                .as_ref()
+                .and_then(|value| value.as_ref())
+                .or(setting.canonical_value.as_ref())
+        {
+            fullscreen_value = Some(value.clone());
+        }
+        changed = true;
+        let revision = setting.option_revision.saturating_add(1) as i64;
+        if let Some(value) = change.canonical_value {
+            let now = Utc::now().timestamp();
+            if let Some(value) = value {
+                let value_json = serde_json::to_string(&value)?;
+                let canonical_type = value.type_name();
+                let kind = if matches!(setting.kind, GameOptionKind::External) {
+                    "external"
+                } else {
+                    "vanilla"
+                };
+                let raw_key = setting.raw_key.as_deref();
+                let value_codec = if setting_by_id(&setting.option_id).is_some()
+                {
+                    "catalog"
+                } else {
+                    "exact_raw"
+                };
+                let source_game_version: Option<&str> = None;
+                sqlx::query(
+                    "INSERT INTO synced_game_option_values
+                        (option_id, kind, raw_key, canonical_type,
+                         canonical_value_json, value_codec, seeded, revision, origin,
+                         source_game_version, source_instance_id, updated_at)
+                    VALUES (?, ?, ?, ?, ?, ?, 1, ?, 'app_editor', ?, NULL, ?)
+                    ON CONFLICT(option_id) DO UPDATE SET
+                        kind = excluded.kind, raw_key = excluded.raw_key,
+                        canonical_type = excluded.canonical_type,
+                        canonical_value_json = excluded.canonical_value_json,
+                        value_codec = excluded.value_codec, seeded = 1,
+                        revision = excluded.revision, origin = 'app_editor',
+                        source_game_version = NULL, source_instance_id = NULL,
+                        updated_at = excluded.updated_at",
+                )
+                .bind(setting.option_id)
+                .bind(kind)
+                .bind(raw_key)
+                .bind(canonical_type)
+                .bind(value_json)
+                .bind(value_codec)
+                .bind(revision)
+                .bind(source_game_version)
+                .bind(now)
+                .execute(&mut *tx)
+                .await?;
+            } else {
+                sqlx::query(
+                    "UPDATE synced_game_option_values
+                    SET canonical_value_json = NULL, seeded = 0, revision = ?,
+                        origin = 'app_editor', source_game_version = NULL,
+                        source_instance_id = NULL, updated_at = ?
+                    WHERE option_id = ?",
+                )
+                .bind(revision)
+                .bind(now)
+                .bind(setting.option_id)
+                .execute(&mut *tx)
+                .await?;
+            }
+        }
+        if let Some(enabled) = change.sync_enabled {
+            sqlx::query(
+                "INSERT INTO synced_game_option_preferences
+                    (option_id, enabled, source, revision)
+                VALUES (?, ?, ?, ?)
+                ON CONFLICT(option_id) DO UPDATE SET
+                    enabled = excluded.enabled, source = 'user',
+                    revision = excluded.revision",
+            )
+            .bind(setting.option_id)
+            .bind(enabled)
+            .bind("user")
+            .bind(revision)
+            .execute(&mut *tx)
+            .await?;
+        }
+    }
+    if changed {
+        let next_revision =
+            current_editor.canonical_revision.saturating_add(1) as i64;
+        let catalog_revision = CATALOG_REVISION as i64;
+        sqlx::query(
+            "INSERT INTO synced_game_option_state (singleton, revision, catalog_revision)
+            VALUES (1, ?, ?)
+            ON CONFLICT(singleton) DO UPDATE SET
+                revision = excluded.revision,
+                catalog_revision = excluded.catalog_revision",
+        )
+        .bind(next_revision)
+        .bind(catalog_revision)
+        .execute(&mut *tx)
+        .await?;
+    }
+    if let Some(value) = fullscreen_value.as_ref() {
+        update_app_fullscreen_setting(&mut tx, value, true).await?;
+    }
+    tx.commit().await?;
+
+    let write_result = if changed {
+        sync_all_participating_instances(&state).await
+    } else {
+        SaveGameSettingsResult {
+            state: None,
+            applied: 0,
+            migrated: 0,
+            deferred: 0,
+            unsupported: 0,
+            failed: 0,
+            conflicts: Vec::new(),
+        }
+    };
+    let result = SaveGameSettingsResult {
+        state: Some(load_settings_editor(&state).await?),
+        conflicts,
+        ..write_result
+    };
+    Ok(result)
+}
@@ -0,0 +1,409 @@
+//! Finds eligible source instances and copies the first shared settings from one.
+
+use super::super as synced_options;
+use super::CATALOG_REVISION;
+use super::api_types::{GameOptionsSourceCandidate, GameOptionsSourceIssue};
+use super::catalog::*;
+use super::fullscreen::update_app_fullscreen_setting;
+use super::launch_overrides::currently_launcher_owned_keys;
+use super::options_file::{
+    input_error, options_path, read_document, validate_raw_key_value,
+};
+use super::read_instance_changes::custom_setting_id;
+use crate::state::{
+    CanonicalValue, InstanceMetadata, State, load_game_option_preferences,
+    load_game_options_sync_state, load_shared_game_options,
+};
+use chrono::Utc;
+
+/// Uses the selected instance's `options.txt` as the initial shared settings.
+pub(in crate::api::instance) async fn initialize_from_source_instance(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<()> {
+    let path = options_path(metadata, state)?;
+    if !path.exists() {
+        return Err(input_error(
+            "Launch the source instance once so Minecraft can create options.txt.",
+        ));
+    }
+    let (document, _) = read_document(&path).await?;
+    let launcher_keys = currently_launcher_owned_keys(metadata);
+    let entries = document.effective_entries();
+    let current_values = load_shared_game_options(&state.pool).await?;
+    let current_preferences = load_game_option_preferences(&state.pool).await?;
+    let (current_revision, _) =
+        load_game_options_sync_state(&state.pool, CATALOG_REVISION).await?;
+    let now = Utc::now().timestamp();
+    let source_version = metadata.applied_content_set.game_version.as_str();
+    let source_id = metadata.instance.id.as_str();
+    let locale_snapshot =
+        if super::locales::has_localizable_mod_settings(&document) {
+            super::locales::capture_observation(metadata, state).await
+        } else {
+            None
+        };
+    let mut tx = state.pool.begin().await?;
+    let catalog_revision = CATALOG_REVISION as i64;
+
+    sqlx::query(
+        "INSERT INTO sync_feature_settings
+            (feature, globally_enabled, new_instance_default)
+        VALUES ('game_options', 1, 1)
+        ON CONFLICT(feature) DO UPDATE SET globally_enabled = 1",
+    )
+    .execute(&mut *tx)
+    .await?;
+    sqlx::query(
+        "INSERT INTO instance_sync_preferences (instance_id, feature, enabled)
+        VALUES (?, 'game_options', 1)
+        ON CONFLICT(instance_id, feature) DO UPDATE SET enabled = 1",
+    )
+    .bind(source_id)
+    .execute(&mut *tx)
+    .await?;
+    sqlx::query(
+        "INSERT INTO synced_game_option_state (singleton, revision, catalog_revision)
+        VALUES (1, 0, ?)
+        ON CONFLICT(singleton) DO UPDATE SET
+            catalog_revision = excluded.catalog_revision",
+    )
+    .bind(catalog_revision)
+    .execute(&mut *tx)
+    .await?;
+    sqlx::query(
+        "UPDATE synced_game_option_values
+         SET seeded = 0, revision = revision + 1, updated_at = ?",
+    )
+    .bind(now)
+    .execute(&mut *tx)
+    .await?;
+    for definition in all_supported_settings() {
+        for key in definition.keys {
+            let custom_id = custom_setting_id(key);
+            let Some(custom) = current_values.get(&custom_id) else {
+                continue;
+            };
+            let revision = custom
+                .revision
+                .max(
+                    current_preferences
+                        .get(&custom_id)
+                        .map(|preference| preference.revision)
+                        .unwrap_or(0),
+                )
+                .saturating_add(1) as i64;
+            sqlx::query(
+                "UPDATE synced_game_option_values
+                SET seeded = 0, revision = ?, updated_at = ?
+                WHERE option_id = ?",
+            )
+            .bind(revision)
+            .bind(now)
+            .bind(custom_id)
+            .execute(&mut *tx)
+            .await?;
+            sqlx::query(
+                "UPDATE synced_game_option_preferences
+                SET enabled = 0, source = 'catalog_default', revision = ?
+                WHERE option_id = ?",
+            )
+            .bind(revision)
+            .bind(custom_id)
+            .execute(&mut *tx)
+            .await?;
+        }
+    }
+    let mut seeded_any = false;
+    let mut fullscreen_value = None;
+    let mut fullscreen_sync_enabled = false;
+
+    for definition in all_supported_settings() {
+        if !supported_settings_cover_game_version(source_version) {
+            break;
+        }
+        let found = definition.keys.iter().find_map(|key| {
+            if launcher_keys.contains(*key) {
+                return None;
+            }
+            let (index, _) = entries.get(*key).copied()?;
+            let entry = document.lines[index].entry.as_ref()?;
+            decode_value_for_version(
+                definition,
+                key,
+                &entry.value,
+                source_version,
+            )
+            .map(|value| ((*key).to_string(), value))
+        });
+        let Some((_physical_key, value)) = found else {
+            continue;
+        };
+        if definition.id == "fullscreen" {
+            fullscreen_value = Some(value.clone());
+            fullscreen_sync_enabled = current_preferences
+                .get(definition.id)
+                .map(|preference| preference.enabled)
+                .unwrap_or(definition.default_on);
+        }
+        seeded_any = true;
+        let option_revision = current_values
+            .get(definition.id)
+            .map(|value| value.revision)
+            .unwrap_or(0)
+            .max(
+                current_preferences
+                    .get(definition.id)
+                    .map(|value| value.revision)
+                    .unwrap_or(0),
+            )
+            .saturating_add(1) as i64;
+        let value_json = serde_json::to_string(&value)?;
+        let canonical_type = value.type_name();
+        sqlx::query(
+            "INSERT INTO synced_game_option_values
+                (option_id, kind, raw_key, canonical_type,
+                 canonical_value_json, value_codec, seeded, revision, origin,
+                 source_game_version, source_instance_id, updated_at)
+            VALUES (?, 'vanilla', NULL, ?, ?, 'catalog', 1, ?,
+                'source_seed', ?, ?, ?)
+            ON CONFLICT(option_id) DO UPDATE SET
+                kind = 'vanilla', raw_key = NULL,
+                canonical_type = excluded.canonical_type,
+                canonical_value_json = excluded.canonical_value_json,
+                value_codec = excluded.value_codec, seeded = 1,
+                revision = excluded.revision, origin = 'source_seed',
+                source_game_version = excluded.source_game_version,
+                source_instance_id = excluded.source_instance_id,
+                updated_at = excluded.updated_at",
+        )
+        .bind(definition.id)
+        .bind(canonical_type)
+        .bind(value_json)
+        .bind(option_revision)
+        .bind(source_version)
+        .bind(source_id)
+        .bind(now)
+        .execute(&mut *tx)
+        .await?;
+        let default_enabled = definition.default_on;
+        sqlx::query(
+            "INSERT INTO synced_game_option_preferences
+                (option_id, enabled, source, revision)
+            VALUES (?, ?, 'catalog_default', ?)
+            ON CONFLICT(option_id) DO NOTHING",
+        )
+        .bind(definition.id)
+        .bind(default_enabled)
+        .bind(option_revision)
+        .execute(&mut *tx)
+        .await?;
+    }
+
+    for (key, (index, _)) in entries {
+        if launcher_keys.contains(key)
+            || setting_by_file_key(key).is_some()
+            || is_never_sync_key(key)
+        {
+            continue;
+        }
+        let Some(entry) = &document.lines[index].entry else {
+            continue;
+        };
+        if validate_raw_key_value(key, &entry.value).is_err() {
+            continue;
+        }
+        let option_id = custom_setting_id(key);
+        let value = CanonicalValue::ExternalRaw(entry.value.clone());
+        seeded_any = true;
+        let option_revision = current_values
+            .get(&option_id)
+            .map(|value| value.revision)
+            .unwrap_or(0)
+            .max(
+                current_preferences
+                    .get(&option_id)
+                    .map(|value| value.revision)
+                    .unwrap_or(0),
+            )
+            .saturating_add(1) as i64;
+        let value_json = serde_json::to_string(&value)?;
+        sqlx::query(
+            "INSERT INTO synced_game_option_values
+                (option_id, kind, raw_key, canonical_type,
+                 canonical_value_json, value_codec, seeded, revision, origin,
+                 source_game_version, source_instance_id, updated_at)
+            VALUES (?, 'external', ?, 'external_raw', ?, 'exact_raw',
+                1, ?, 'source_seed', ?, ?, ?)
+            ON CONFLICT(option_id) DO UPDATE SET
+                raw_key = excluded.raw_key,
+                canonical_value_json = excluded.canonical_value_json,
+                seeded = 1, revision = excluded.revision,
+                origin = 'source_seed',
+                source_game_version = excluded.source_game_version,
+                source_instance_id = excluded.source_instance_id,
+                updated_at = excluded.updated_at",
+        )
+        .bind(option_id)
+        .bind(key)
+        .bind(value_json)
+        .bind(option_revision)
+        .bind(source_version)
+        .bind(source_id)
+        .bind(now)
+        .execute(&mut *tx)
+        .await?;
+        sqlx::query(
+            "
+			INSERT INTO synced_game_option_preferences
+				(option_id, enabled, source, revision)
+			VALUES (?, 0, 'discovery_default', ?)
+			ON CONFLICT(option_id) DO NOTHING
+			",
+        )
+        .bind(option_id)
+        .bind(option_revision)
+        .execute(&mut *tx)
+        .await?;
+    }
+    if !seeded_any {
+        return Err(input_error(
+            "The selected options.txt has no settings that can be safely used as a sync baseline.",
+        ));
+    }
+
+    let next_revision = current_revision.saturating_add(1) as i64;
+    sqlx::query(
+        "UPDATE synced_game_option_state
+        SET revision = ?, catalog_revision = ?
+        WHERE singleton = 1",
+    )
+    .bind(next_revision)
+    .bind(catalog_revision)
+    .execute(&mut *tx)
+    .await?;
+    if let Some(value) = fullscreen_value.as_ref() {
+        update_app_fullscreen_setting(&mut tx, value, fullscreen_sync_enabled)
+            .await?;
+    }
+    super::locales::record_observations(
+        &mut tx,
+        metadata,
+        &document,
+        locale_snapshot.as_deref(),
+    )
+    .await;
+    tx.commit().await?;
+    super::locales::queue_game_locale_index();
+    Ok(())
+}
+
+pub async fn list_sync_sources()
+-> crate::Result<Vec<GameOptionsSourceCandidate>> {
+    let state = State::get().await?;
+    let _guard = state.lock_synced_options().await;
+    let instances = crate::state::list_instances(&state.pool).await?;
+    let mut sources = Vec::with_capacity(instances.len());
+    for metadata in instances {
+        let path = options_path(&metadata, &state)?;
+        let version_supported = supported_settings_cover_game_version(
+            &metadata.applied_content_set.game_version,
+        );
+        let mut eligible = true;
+        let mut disabled_reason = None;
+        let mut recognized_setting_count = 0;
+        let mut custom_setting_count = 0;
+        let installing = synced_options::sync_files_are_protected(&metadata);
+        if !installing && !path.exists() {
+            eligible = false;
+            disabled_reason = Some(GameOptionsSourceIssue::MissingOptionsFile);
+        } else if !installing {
+            match read_document(&path).await {
+                Ok((document, _)) => {
+                    let launcher_keys =
+                        currently_launcher_owned_keys(&metadata);
+                    let entries = document.effective_entries();
+                    let source_version =
+                        metadata.applied_content_set.game_version.as_str();
+                    let recognized = if version_supported {
+                        all_supported_settings()
+                            .filter(|setting| {
+                                setting.keys.iter().any(|key| {
+                                    if launcher_keys.contains(*key) {
+                                        return false;
+                                    }
+                                    document.value(key).is_some_and(|raw| {
+                                        decode_value_for_version(
+                                            setting,
+                                            key,
+                                            raw,
+                                            source_version,
+                                        )
+                                        .is_some()
+                                    })
+                                })
+                            })
+                            .count()
+                    } else {
+                        0
+                    };
+                    let custom = entries
+                        .into_iter()
+                        .filter(|(key, (index, _))| {
+                            !launcher_keys.contains(*key)
+                                && setting_by_file_key(key).is_none()
+                                && !is_never_sync_key(key)
+                                && document.lines[*index]
+                                    .entry
+                                    .as_ref()
+                                    .is_some_and(|entry| {
+                                        validate_raw_key_value(
+                                            key,
+                                            &entry.value,
+                                        )
+                                        .is_ok()
+                                    })
+                        })
+                        .count();
+                    if recognized + custom == 0 {
+                        eligible = false;
+                        disabled_reason = Some(if version_supported {
+                            GameOptionsSourceIssue::NoSyncableSettings
+                        } else {
+                            GameOptionsSourceIssue::UnsupportedVersion
+                        });
+                    } else {
+                        recognized_setting_count = recognized as u32;
+                        custom_setting_count = custom as u32;
+                    }
+                }
+                Err(error) => {
+                    tracing::warn!(
+                        "Could not inspect {} as a game-settings source: {error}",
+                        metadata.instance.id
+                    );
+                    eligible = false;
+                    disabled_reason =
+                        Some(GameOptionsSourceIssue::UnreadableOptionsFile);
+                }
+            }
+        }
+        sources.push(GameOptionsSourceCandidate {
+            source_id: metadata.instance.id.clone(),
+            instance_id: metadata.instance.id,
+            name: metadata.instance.name,
+            icon_path: metadata.instance.icon_path,
+            game_version: Some(metadata.applied_content_set.game_version),
+            eligible,
+            disabled_reason,
+            recognized_setting_count,
+            custom_setting_count,
+        });
+    }
+    sources.sort_by(|left, right| {
+        left.name
+            .cmp(&right.name)
+            .then(left.instance_id.cmp(&right.instance_id))
+    });
+    Ok(sources)
+}
@@ -0,0 +1,393 @@
+//! Imports `options.txt` saves and copies canonical values to synced instances.
+
+use super::super as synced_options;
+use super::CATALOG_REVISION;
+use super::api_types::{
+    GameOptionMappingKind, SaveGameSettingsResult, SyncOutcome,
+};
+use super::catalog::*;
+use super::options_file::{
+    GameOptionsDocument, options_path, read_document, sha1_bytes,
+};
+use super::pack_updates::materialize_yosbr_options_if_missing;
+use super::read_instance_changes::read_instance_changes_into_shared_settings;
+use super::source_selection::initialize_from_source_instance;
+use crate::state::{
+    CanonicalValue, InstanceMetadata, State, SyncedOption,
+    game_options_sync_is_enabled, load_game_option_preferences,
+    load_game_options_sync_state, load_shared_game_options,
+};
+use crate::util::io;
+
+struct AppliedSettings {
+    count: usize,
+    used_migration: bool,
+}
+
+pub(super) async fn sync_is_active_for_instance(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<bool> {
+    Ok(metadata.synced_options.game_options
+        && !synced_options::pending::contains(
+            &metadata.instance.id,
+            SyncedOption::GameOptions,
+            state,
+        )
+        .await?
+        && game_options_sync_is_enabled(&state.pool).await?)
+}
+
+pub(super) async fn remember_processed_sha(
+    instance_id: &str,
+    sha1: &str,
+    state: &State,
+) -> crate::Result<()> {
+    let (canonical_revision, _) =
+        load_game_options_sync_state(&state.pool, CATALOG_REVISION).await?;
+    synced_options::begin_checkpoint(
+        instance_id,
+        SyncedOption::GameOptions,
+        "default",
+        sha1,
+        None,
+        canonical_revision as i64,
+        state,
+    )
+    .await?;
+    synced_options::finish_plain_checkpoint(
+        instance_id,
+        SyncedOption::GameOptions,
+        "default",
+        state,
+    )
+    .await
+}
+
+async fn apply_shared_settings_to_document(
+    metadata: &InstanceMetadata,
+    document: &mut GameOptionsDocument,
+    state: &State,
+) -> crate::Result<AppliedSettings> {
+    let values = load_shared_game_options(&state.pool).await?;
+    let preferences = load_game_option_preferences(&state.pool).await?;
+    let mut count = 0;
+    let mut used_migration = false;
+
+    for (option_id, preference) in preferences {
+        if !preference.enabled {
+            continue;
+        }
+        if option_id == "fullscreen"
+            && metadata.launch_overrides.force_fullscreen.is_some()
+        {
+            continue;
+        }
+        let Some(stored) = values.get(&option_id) else {
+            continue;
+        };
+        let Some(value) = stored.value.as_ref().filter(|_| stored.seeded)
+        else {
+            continue;
+        };
+        let definition = setting_by_id(&option_id);
+        if definition.is_some()
+            && !supported_settings_cover_game_version(
+                &metadata.applied_content_set.game_version,
+            )
+        {
+            continue;
+        }
+        if definition.is_none()
+            && stored
+                .raw_key
+                .as_deref()
+                .is_some_and(|key| setting_by_file_key(key).is_some())
+        {
+            continue;
+        }
+
+        let target_version = &metadata.applied_content_set.game_version;
+        let key =
+            target_physical_key(definition, stored, document, target_version)
+                .or_else(|| {
+                    definition.and_then(|definition| {
+                        target_key_for_version(definition, target_version)
+                            .map(str::to_string)
+                    })
+                })
+                .or_else(|| stored.raw_key.clone());
+        let Some(key) = key else {
+            continue;
+        };
+
+        let migrated = definition.is_some_and(|definition| {
+            alias_migration_needed(definition, document, &key)
+                || document.value(&key).is_some_and(|raw| {
+                    !physical_representation_supported_for_target(
+                        definition,
+                        &key,
+                        raw,
+                        target_version,
+                    )
+                })
+        });
+        let raw_value = if let Some(definition) = definition {
+            let Some(raw_value) = encode_value(
+                definition,
+                &key,
+                value,
+                target_version,
+                document.value(&key),
+            ) else {
+                continue;
+            };
+            raw_value
+        } else if let CanonicalValue::ExternalRaw(raw_value) = value {
+            raw_value.clone()
+        } else {
+            continue;
+        };
+
+        document.set(&key, &raw_value, true)?;
+        count += 1;
+        used_migration |= migrated
+            || definition.is_some_and(|definition| {
+                (matches!(definition.encoding, ValueEncoding::KeyBinding)
+                    && split_key_binding(&raw_value).0.parse::<i32>().is_ok())
+                    || physical_variant_for_present_key(
+                        definition,
+                        &key,
+                        target_version,
+                    )
+                    .map(|variant| {
+                        variant.mapping != GameOptionMappingKind::Direct
+                    })
+                    .unwrap_or_else(|| {
+                        definition.keys.first().copied() != Some(key.as_str())
+                    })
+            });
+    }
+
+    Ok(AppliedSettings {
+        count,
+        used_migration,
+    })
+}
+
+pub(super) async fn apply_shared_settings_to_instance(
+    metadata: &InstanceMetadata,
+    state: &State,
+    allow_protected: bool,
+) -> crate::Result<SyncOutcome> {
+    if !allow_protected && synced_options::sync_files_are_protected(metadata) {
+        return Ok(SyncOutcome::Deferred);
+    }
+    if !sync_is_active_for_instance(metadata, state).await? {
+        return Ok(SyncOutcome::Unchanged);
+    }
+
+    let path = options_path(metadata, state)?;
+    if !path.exists() {
+        materialize_yosbr_options_if_missing(metadata, state).await?;
+    }
+    let file_was_missing = !path.exists();
+    let (mut document, input_bytes) = if path.exists() {
+        read_document(&path).await?
+    } else {
+        let Some(document) =
+            GameOptionsDocument::for_instance(metadata, state).await?
+        else {
+            return Ok(SyncOutcome::WaitingForFile);
+        };
+        (document, Vec::new())
+    };
+    if document.value("version").is_none()
+        && !supported_settings_cover_game_version(
+            &metadata.applied_content_set.game_version,
+        )
+    {
+        return Ok(SyncOutcome::Deferred);
+    }
+    let applied =
+        apply_shared_settings_to_document(metadata, &mut document, state)
+            .await?;
+    if file_was_missing && applied.count == 0 {
+        return Ok(SyncOutcome::WaitingForFile);
+    }
+
+    let output_bytes = document.serialize()?;
+    let output_sha1 = sha1_bytes(&output_bytes);
+    let changed = file_was_missing || output_bytes != input_bytes;
+
+    // Register the expected bytes before touching the file. The filesystem
+    // watcher can observe the write immediately on some platforms; recording
+    // the checkpoint first prevents that event from being misclassified as a
+    // user edit and importing stale data back into the shared store.
+    synced_options::begin_checkpoint(
+        &metadata.instance.id,
+        SyncedOption::GameOptions,
+        "default",
+        &output_sha1,
+        None,
+        load_game_options_sync_state(&state.pool, CATALOG_REVISION)
+            .await?
+            .0 as i64,
+        state,
+    )
+    .await?;
+    if changed {
+        io::write(&path, output_bytes).await?;
+    }
+    synced_options::finish_plain_checkpoint(
+        &metadata.instance.id,
+        SyncedOption::GameOptions,
+        "default",
+        state,
+    )
+    .await?;
+
+    Ok(if changed && applied.used_migration {
+        SyncOutcome::Migrated
+    } else if changed {
+        SyncOutcome::Applied
+    } else {
+        SyncOutcome::Unchanged
+    })
+}
+
+pub(super) async fn capture_instance_options(
+    metadata: &InstanceMetadata,
+    state: &State,
+    allow_protected: bool,
+) -> crate::Result<SyncOutcome> {
+    if !allow_protected && synced_options::sync_files_are_protected(metadata) {
+        return Ok(SyncOutcome::Deferred);
+    }
+    if !sync_is_active_for_instance(metadata, state).await? {
+        return Ok(SyncOutcome::Unchanged);
+    }
+
+    let path = options_path(metadata, state)?;
+    if !path.exists() {
+        return Ok(SyncOutcome::WaitingForFile);
+    }
+    let (document, input_bytes) = read_document(&path).await?;
+    let input_sha1 = sha1_bytes(&input_bytes);
+    let checkpoint = synced_options::checkpoint(
+        &metadata.instance.id,
+        SyncedOption::GameOptions,
+        "default",
+        state,
+    )
+    .await?;
+    if checkpoint
+        .as_ref()
+        .is_some_and(|checkpoint| checkpoint.expected_sha1 == input_sha1)
+    {
+        return Ok(SyncOutcome::Unchanged);
+    }
+
+    let canonical_changed =
+        if crate::state::shared_game_options_exist(&state.pool).await? {
+            read_instance_changes_into_shared_settings(
+                metadata, &document, state,
+            )
+            .await?
+        } else {
+            initialize_from_source_instance(metadata, state).await?;
+            true
+        };
+    remember_processed_sha(&metadata.instance.id, &input_sha1, state).await?;
+
+    if canonical_changed {
+        let _ = sync_other_participating_instances(
+            state,
+            Some(&metadata.instance.id),
+        )
+        .await;
+    }
+    Ok(SyncOutcome::Unchanged)
+}
+
+pub(in crate::api::instance) async fn capture_instance_file_change(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<()> {
+    capture_instance_options(metadata, state, false).await?;
+    Ok(())
+}
+
+pub(in crate::api::instance) async fn apply_instance_with_state(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<()> {
+    apply_shared_settings_to_instance(metadata, state, false).await?;
+    Ok(())
+}
+
+pub(super) async fn sync_other_participating_instances(
+    state: &State,
+    excluded_instance_id: Option<&str>,
+) -> SaveGameSettingsResult {
+    let mut result = SaveGameSettingsResult {
+        state: None,
+        applied: 0,
+        migrated: 0,
+        deferred: 0,
+        unsupported: 0,
+        failed: 0,
+        conflicts: Vec::new(),
+    };
+    match game_options_sync_is_enabled(&state.pool).await {
+        Ok(true) => {}
+        Ok(false) => return result,
+        Err(error) => {
+            tracing::warn!(
+                "Failed to inspect global game-options state before fan-out: {error}"
+            );
+            result.failed += 1;
+            return result;
+        }
+    }
+    let instances = match crate::state::list_instances(&state.pool).await {
+        Ok(instances) => instances,
+        Err(error) => {
+            tracing::warn!(
+                "Failed to list instances for game-options fan-out: {error}"
+            );
+            result.failed += 1;
+            return result;
+        }
+    };
+    for metadata in instances {
+        if excluded_instance_id == Some(metadata.instance.id.as_str())
+            || !metadata.synced_options.game_options
+        {
+            continue;
+        }
+        match apply_shared_settings_to_instance(&metadata, state, false).await {
+            Ok(SyncOutcome::Applied | SyncOutcome::Unchanged) => {
+                result.applied += 1
+            }
+            Ok(SyncOutcome::Migrated) => result.migrated += 1,
+            Ok(SyncOutcome::Deferred | SyncOutcome::WaitingForFile) => {
+                result.deferred += 1
+            }
+            Err(error) => {
+                tracing::warn!(
+                    "Failed to write synced game options into {}: {error}",
+                    metadata.instance.id
+                );
+                result.failed += 1;
+            }
+        }
+    }
+    result
+}
+
+pub(crate) async fn sync_all_participating_instances(
+    state: &State,
+) -> SaveGameSettingsResult {
+    sync_other_participating_instances(state, None).await
+}
@@ -0,0 +1,14 @@
+mod files;
+mod game_options;
+pub(in crate::api::instance) mod pending;
+
+const COMMAND_HISTORY_FILE: &str = "command_history.txt";
+const HOTBAR_FILE: &str = "hotbar.nbt";
+
+pub(super) use self::files::{
+    CheckpointStatus, begin_checkpoint, checkpoint, detach_link, ensure_link,
+    finish_checkpoint, finish_plain_checkpoint, instance_game_dir,
+    instance_is_running, instance_option_enabled, nbt_from_bytes, nbt_to_bytes,
+    option_can_apply_while_running, read_nbt_file, safe_instance_id,
+    sha1_bytes, sha1_file, sync_files_are_protected, synced_options_path,
+};
@@ -0,0 +1,104 @@
+use super::files::synced_options_path;
+use crate::State;
+use crate::state::SyncedOption;
+use crate::util::io;
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Copy, Debug, Deserialize, Eq, PartialEq, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum SyncedOptionJoinResolution {
+    UseSynced,
+    UseInstance,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "action", rename_all = "snake_case")]
+pub(super) enum PendingAction {
+    SelectSource,
+    Join {
+        resolution: Option<SyncedOptionJoinResolution>,
+    },
+}
+
+#[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
+pub(super) struct PendingChange {
+    pub instance_id: String,
+    pub option: SyncedOption,
+    pub action: PendingAction,
+}
+
+pub(super) async fn read(state: &State) -> crate::Result<Vec<PendingChange>> {
+    let path = synced_options_path(state).join("pending-changes.json");
+    match tokio::fs::read(path).await {
+        Ok(bytes) => Ok(serde_json::from_slice(&bytes)?),
+        Err(error) if error.kind() == std::io::ErrorKind::NotFound => {
+            Ok(Vec::new())
+        }
+        Err(error) => Err(error.into()),
+    }
+}
+
+async fn write(changes: &[PendingChange], state: &State) -> crate::Result<()> {
+    let directory = synced_options_path(state);
+    io::create_dir_all(&directory).await?;
+    let temporary = directory.join("pending-changes.json.tmp");
+    io::write(&temporary, serde_json::to_vec(changes)?).await?;
+    tokio::fs::rename(temporary, directory.join("pending-changes.json"))
+        .await?;
+    Ok(())
+}
+
+/// Callers hold the synced-options lock while updating or replaying requests.
+pub(super) async fn save(
+    change: PendingChange,
+    state: &State,
+) -> crate::Result<()> {
+    let mut changes = read(state).await?;
+    changes.retain(|previous| {
+        previous.option != change.option
+            || (change.action != PendingAction::SelectSource
+                && previous.instance_id != change.instance_id)
+    });
+    changes.push(change);
+    write(&changes, state).await
+}
+
+pub(super) async fn remove(
+    change: &PendingChange,
+    state: &State,
+) -> crate::Result<()> {
+    let mut changes = read(state).await?;
+    let previous_len = changes.len();
+    changes.retain(|previous| previous != change);
+    if changes.len() != previous_len {
+        write(&changes, state).await?;
+    }
+    Ok(())
+}
+
+pub(super) async fn cancel(
+    option: SyncedOption,
+    instance_id: Option<&str>,
+    state: &State,
+) -> crate::Result<()> {
+    let mut changes = read(state).await?;
+    let previous_len = changes.len();
+    changes.retain(|change| {
+        change.option != option
+            || instance_id.is_some_and(|id| change.instance_id != id)
+    });
+    if changes.len() != previous_len {
+        write(&changes, state).await?;
+    }
+    Ok(())
+}
+
+pub(in crate::api::instance) async fn contains(
+    instance_id: &str,
+    option: SyncedOption,
+    state: &State,
+) -> crate::Result<bool> {
+    Ok(read(state).await?.iter().any(|change| {
+        change.instance_id == instance_id && change.option == option
+    }))
+}
@@ -0,0 +1,112 @@
+use super::super::synced_options::{
+    nbt_from_bytes, nbt_to_bytes, read_nbt_file,
+};
+use crate::ErrorKind;
+use quartz_nbt::{NbtCompound, NbtList, NbtTag};
+use std::path::Path;
+
+pub(crate) async fn read_servers(
+    path: &Path,
+) -> crate::Result<Vec<NbtCompound>> {
+    if !path.exists() {
+        return Ok(Vec::new());
+    }
+    servers_from_root(read_nbt_file(path).await?)
+}
+
+pub(super) fn servers_from_bytes(
+    bytes: Vec<u8>,
+) -> crate::Result<Vec<NbtCompound>> {
+    servers_from_root(nbt_from_bytes(bytes)?)
+}
+
+fn servers_from_root(root: NbtCompound) -> crate::Result<Vec<NbtCompound>> {
+    let list = root.get::<_, &NbtList>("servers").map_err(|_| {
+        ErrorKind::InputError(
+            "servers.dat does not contain a valid servers list".to_string(),
+        )
+    })?;
+    list.iter()
+        .map(|tag| match tag {
+            NbtTag::Compound(compound) => Ok(compound.clone()),
+            _ => Err(ErrorKind::InputError(
+                "servers.dat contains an invalid server entry".to_string(),
+            )
+            .into()),
+        })
+        .collect()
+}
+
+pub(crate) async fn write_servers(
+    path: &Path,
+    servers: &[NbtCompound],
+) -> crate::Result<()> {
+    if let Some(parent) = path.parent() {
+        crate::util::io::create_dir_all(parent).await?;
+    }
+    crate::util::io::write(path, servers_to_bytes(servers)?).await?;
+    Ok(())
+}
+
+pub(super) fn servers_to_bytes(
+    servers: &[NbtCompound],
+) -> crate::Result<Vec<u8>> {
+    let mut list = NbtList::new();
+    for server in servers {
+        list.push(server.clone());
+    }
+    let mut root = NbtCompound::new();
+    root.insert("servers", list);
+    nbt_to_bytes(&root)
+}
+
+pub(crate) fn server_data(
+    name: String,
+    address: String,
+    accept_textures: Option<bool>,
+) -> NbtCompound {
+    let mut server = NbtCompound::new();
+    server.insert("name", name);
+    server.insert("ip", address);
+    if let Some(accept_textures) = accept_textures {
+        server.insert("acceptTextures", i8::from(accept_textures));
+    }
+    server.insert("hidden", 0_i8);
+    server
+}
+
+pub(super) fn update_server_data(
+    server: &mut NbtCompound,
+    name: String,
+    address: String,
+    accept_textures: Option<bool>,
+) {
+    server.insert("name", name);
+    server.insert("ip", address);
+    match accept_textures {
+        Some(value) => server.insert("acceptTextures", i8::from(value)),
+        None => {
+            server.inner_mut().remove("acceptTextures");
+        }
+    }
+}
+
+pub(super) fn server_hidden(server: &NbtCompound) -> bool {
+    server.get::<_, i8>("hidden").unwrap_or(0) != 0
+}
+
+pub(super) fn server_address(server: &NbtCompound) -> String {
+    server.get::<_, &str>("ip").unwrap_or_default().to_string()
+}
+
+pub(super) fn server_identity_address(server: &NbtCompound) -> String {
+    server_address(server).trim().to_ascii_lowercase()
+}
+
+pub(super) fn server_identity_name(server: &NbtCompound) -> String {
+    server
+        .get::<_, &str>("name")
+        .unwrap_or_default()
+        .trim()
+        .to_ascii_lowercase()
+}
@@ -0,0 +1,24 @@
+mod codec;
+mod modpack;
+mod operations;
+mod storage;
+mod types;
+
+const SERVERS_FILE: &str = "servers.dat";
+
+pub(crate) use self::codec::server_data;
+pub use self::modpack::{capture_modpack_servers, clear_modpack_servers};
+pub(crate) use self::operations::{
+    add_user_server, ensure_managed_server, list_server_records,
+    remove_server_by_index, update_server_by_index,
+};
+pub use self::operations::{
+    desync_server, list_synced_servers, remove_synced_server,
+    update_synced_server,
+};
+pub(super) use self::operations::{
+    detach_servers, ensure_servers, merge_servers_from_instance,
+    reconcile_servers, seed_servers,
+};
+pub(super) use self::storage::canonical_exists;
+pub use self::types::{DesyncServerMode, ServerSource, SyncedServer};
@@ -0,0 +1,219 @@
+use super::super::synced_options::instance_game_dir;
+use super::SERVERS_FILE;
+use super::codec::{read_servers, servers_from_bytes};
+use super::operations::{compose_instance, effective};
+use super::storage::{load_local, write_local_rows};
+use super::types::{LocalServer, ServerSource};
+use crate::state::{CachedEntry, InstanceLink, InstanceMetadata};
+use crate::util::fetch::{DownloadMeta, DownloadReason, fetch};
+use crate::{ErrorKind, State};
+use async_zip::base::read::seek::ZipFileReader;
+use quartz_nbt::NbtCompound;
+use std::io::Cursor;
+use uuid::Uuid;
+
+pub async fn capture_modpack_servers(instance_id: &str) -> crate::Result<()> {
+    let state = State::get().await?;
+    let _guard = state.lock_synced_options().await;
+    let metadata = crate::state::get_instance(instance_id, &state.pool)
+        .await?
+        .ok_or_else(|| ErrorKind::InputError("Unknown instance".to_string()))?;
+    let path = instance_game_dir(&metadata, &state)?.join(SERVERS_FILE);
+    let servers = read_servers(&path).await?;
+    replace_modpack_servers(&metadata, servers, &state).await?;
+    if effective(&metadata, &state).await? {
+        compose_instance(&metadata, &state).await?;
+    }
+    Ok(())
+}
+
+pub async fn clear_modpack_servers(instance_id: &str) -> crate::Result<()> {
+    let state = State::get().await?;
+    let _guard = state.lock_synced_options().await;
+    let metadata = crate::state::get_instance(instance_id, &state.pool)
+        .await?
+        .ok_or_else(|| ErrorKind::InputError("Unknown instance".to_string()))?;
+    replace_modpack_servers(&metadata, Vec::new(), &state).await?;
+    if effective(&metadata, &state).await? {
+        compose_instance(&metadata, &state).await?;
+    }
+    Ok(())
+}
+
+async fn replace_modpack_servers(
+    metadata: &InstanceMetadata,
+    servers: Vec<NbtCompound>,
+    state: &State,
+) -> crate::Result<()> {
+    let mut local = servers
+        .into_iter()
+        .enumerate()
+        .map(|(position, data)| LocalServer {
+            id: Uuid::new_v4().to_string(),
+            source: ServerSource::Modpack,
+            excluded_synced_server_id: None,
+            data,
+            position: position as i64,
+        })
+        .collect::<Vec<_>>();
+    let mut retained = load_local(&metadata.instance.id, state)
+        .await?
+        .into_iter()
+        .filter(|server| server.source != ServerSource::Modpack)
+        .collect::<Vec<_>>();
+    for server in &mut retained {
+        server.position = local.len() as i64;
+        local.push(server.clone());
+    }
+    let mut tx = state.pool.begin().await?;
+    write_local_rows(&mut tx, &metadata.instance.id, &local).await?;
+    let version_id = modpack_version_id(&metadata.link);
+    sqlx::query(
+        "INSERT INTO instance_server_pack_state (instance_id, version_id)
+        VALUES (?, ?)
+        ON CONFLICT(instance_id) DO UPDATE SET
+            version_id = excluded.version_id",
+    )
+    .bind(metadata.instance.id)
+    .bind(version_id)
+    .execute(&mut *tx)
+    .await?;
+    tx.commit().await?;
+    Ok(())
+}
+
+pub(super) async fn pack_state_matches_link(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<bool> {
+    let row = sqlx::query(
+        "SELECT version_id
+        FROM instance_server_pack_state
+        WHERE instance_id = ?",
+    )
+    .bind(metadata.instance.id)
+    .fetch_optional(&state.pool)
+    .await?;
+    Ok(row.is_some_and(|row| {
+        use sqlx::Row;
+        let version_id: Option<String> = row.get("version_id");
+        version_id.as_deref() == modpack_version_id(&metadata.link)
+    }))
+}
+
+pub(super) async fn pack_state_exists(
+    instance_id: &str,
+    state: &State,
+) -> crate::Result<bool> {
+    Ok(sqlx::query_scalar::<_, bool>(
+        "SELECT EXISTS(
+            SELECT 1 FROM instance_server_pack_state WHERE instance_id = ?
+        )",
+    )
+    .bind(instance_id)
+    .fetch_one(&state.pool)
+    .await?)
+}
+
+pub(super) async fn reconstruct_modpack_servers(
+    metadata: &InstanceMetadata,
+    state: &State,
+) -> crate::Result<()> {
+    let version_id = modpack_version_id(&metadata.link).ok_or_else(|| {
+        ErrorKind::InputError(
+            "This modpack does not have a recoverable Modrinth version."
+                .to_string(),
+        )
+    })?;
+    let typed_version_id =
+        crate::state::ModrinthVersionId::new(version_id.to_string())?;
+    let version = CachedEntry::get_version(
+        &typed_version_id,
+        None,
+        &state.pool,
+        &state.api_semaphore,
+    )
+    .await?
+    .ok_or_else(|| {
+        ErrorKind::InputError(format!(
+            "Modpack version {version_id} could not be found"
+        ))
+    })?;
+    let primary_file = version
+        .files
+        .iter()
+        .find(|file| file.primary)
+        .or_else(|| version.files.first())
+        .ok_or_else(|| {
+            ErrorKind::InputError(format!(
+                "Modpack version {version_id} has no downloadable file"
+            ))
+        })?;
+    let download_meta = DownloadMeta {
+        reason: DownloadReason::Modpack,
+        game_version: metadata.applied_content_set.game_version.clone(),
+        loader: metadata.applied_content_set.loader.as_str().to_string(),
+        dependent_on: Some(version_id.to_string()),
+    };
+    let mrpack = fetch(
+        &primary_file.url,
+        primary_file.hashes.get("sha1").map(String::as_str),
+        Some(&download_meta),
+        None,
+        &state.api_semaphore,
+        &state.pool,
+    )
+    .await?;
+    let mut archive = ZipFileReader::with_tokio(Cursor::new(&mrpack)).await?;
+    let mut selected = None;
+    for (index, entry) in archive.file().entries().iter().enumerate() {
+        let Ok(filename) = entry.filename().as_str() else {
+            continue;
+        };
+        let priority = if filename == "client-overrides/servers.dat" {
+            2
+        } else if filename == "overrides/servers.dat" {
+            1
+        } else {
+            continue;
+        };
+        if selected
+            .is_none_or(|(selected_priority, _)| priority >= selected_priority)
+        {
+            selected = Some((priority, index));
+        }
+    }
+
+    let servers = if let Some((_, index)) = selected {
+        let mut bytes = Vec::new();
+        let mut reader = archive.reader_with_entry(index).await?;
+        reader.read_to_end_checked(&mut bytes).await?;
+        servers_from_bytes(bytes)?
+    } else {
+        Vec::new()
+    };
+    replace_modpack_servers(metadata, servers, state).await
+}
+
+pub(super) fn is_modpack_link(link: &InstanceLink) -> bool {
+    matches!(
+        link,
+        InstanceLink::ModrinthModpack { .. }
+            | InstanceLink::ServerProjectModpack { .. }
+            | InstanceLink::ImportedModpack { .. }
+    )
+}
+
+fn modpack_version_id(link: &InstanceLink) -> Option<&str> {
+    match link {
+        InstanceLink::ModrinthModpack { version_id, .. } => Some(version_id),
+        InstanceLink::ServerProjectModpack {
+            content_version_id, ..
+        } => Some(content_version_id),
+        InstanceLink::ImportedModpack {
+            version_id: Some(version_id),
+            ..
+        } => Some(version_id),
+        _ => None,
+    }
+}
@@ -0,0 +1,369 @@
+use super::super::synced_options::{
+    nbt_from_bytes, nbt_to_bytes, safe_instance_id, synced_options_path,
+};
+use super::SERVERS_FILE;
+use super::types::{
+    CanonicalServer, LocalServer, ProjectionEntry, ProjectionOwner,
+    ServerRecord, ServerSource,
+};
+use crate::{ErrorKind, State};
+use sqlx::{Executor, Sqlite, Transaction};
+use std::collections::HashSet;
+use std::path::PathBuf;
+
+pub(in crate::api::instance) async fn canonical_exists(
+    state: &State,
+) -> crate::Result<bool> {
+    canonical_initialized(state).await
+}
+
+async fn canonical_initialized(state: &State) -> crate::Result<bool> {
+    Ok(sqlx::query_scalar::<_, bool>(
+        "SELECT EXISTS(
+            SELECT 1 FROM synced_server_state WHERE singleton = 1
+        )",
+    )
+    .fetch_one(&state.pool)
+    .await?)
+}
+
+pub(super) async fn read_canonical(
+    state: &State,
+) -> crate::Result<Vec<CanonicalServer>> {
+    read_canonical_with(&state.pool).await
+}
+
+async fn read_canonical_with<'e>(
+    executor: impl Executor<'e, Database = Sqlite>,
+) -> crate::Result<Vec<CanonicalServer>> {
+    let rows = sqlx::query(
+        "SELECT id, nbt
+        FROM synced_servers
+        ORDER BY position",
+    )
+    .fetch_all(executor)
+    .await?;
+    use sqlx::Row;
+    rows.into_iter()
+        .map(|row| {
+            let id: String = row.get("id");
+            let nbt: Vec<u8> = row.get("nbt");
+            Ok(CanonicalServer {
+                id,
+                data: nbt_from_bytes(nbt)?,
+            })
+        })
+        .collect()
+}
+
+/// Reads canonical servers and instance overrides from the same committed revision.
+pub(super) async fn read_server_snapshot(
+    instance_id: &str,
+    state: &State,
+) -> crate::Result<(Vec<CanonicalServer>, Vec<LocalServer>)> {
+    let mut tx = state.pool.begin().await?;
+    let canonical = read_canonical_with(&mut *tx).await?;
+    let local = load_local_with(instance_id, &mut *tx).await?;
+    tx.commit().await?;
+    Ok((canonical, local))
+}
+
+pub(super) async fn commit_server_state(
+    canonical: Option<&[CanonicalServer]>,
+    local: Option<(&str, &[LocalServer])>,
+    state: &State,
+) -> crate::Result<bool> {
+    let mut tx = state.pool.begin().await?;
+    let mut canonical_changed = false;
+    if let Some(canonical) = canonical {
+        canonical_changed = write_canonical_rows(&mut tx, canonical).await?;
+        sqlx::query(
+            "INSERT INTO synced_server_state (singleton, revision)
+            VALUES (1, 0)
+            ON CONFLICT(singleton) DO NOTHING",
+        )
+        .execute(&mut *tx)
+        .await?;
+        if canonical_changed {
+            sqlx::query(
+                "UPDATE synced_server_state
+                SET revision = revision + 1
+                WHERE singleton = 1",
+            )
+            .execute(&mut *tx)
+            .await?;
+        }
+    }
+    if let Some((instance_id, local)) = local {
+        write_local_rows(&mut tx, instance_id, local).await?;
+    }
+    tx.commit().await?;
+    Ok(canonical_changed)
+}
+
+async fn write_canonical_rows(
+    tx: &mut Transaction<'_, Sqlite>,
+    servers: &[CanonicalServer],
+) -> crate::Result<bool> {
+    let current = sqlx::query(
+        "SELECT id, position, nbt
+        FROM synced_servers
+        ORDER BY position",
+    )
+    .fetch_all(&mut **tx)
+    .await?;
+    let mut desired = Vec::with_capacity(servers.len());
+    for (position, server) in servers.iter().enumerate() {
+        desired.push((
+            server.id.as_str(),
+            position as i64,
+            nbt_to_bytes(&server.data)?,
+        ));
+    }
+    if current.len() == desired.len()
+        && current.iter().zip(&desired).all(|(current, desired)| {
+            current.id == desired.0
+                && current.position == desired.1
+                && current.nbt == desired.2
+        })
+    {
+        return Ok(false);
+    }
+
+    let desired_ids =
+        desired.iter().map(|(id, _, _)| *id).collect::<HashSet<_>>();
+    for row in &current {
+        if !desired_ids.contains(row.id.as_str()) {
+            sqlx::query("DELETE FROM synced_servers WHERE id = ?")
+                .bind(&row.id)
+                .execute(&mut **tx)
+                .await?;
+        }
+    }
+
+    let position_offset = current
+        .iter()
+        .map(|row| row.position)
+        .max()
+        .unwrap_or(0)
+        .max(servers.len() as i64)
+        .saturating_add(1);
+    sqlx::query("UPDATE synced_servers SET position = position + ?")
+        .bind(position_offset)
+        .execute(&mut **tx)
+        .await?;
+
+    for (id, position, nbt) in desired {
+        sqlx::query(
+            "INSERT INTO synced_servers (id, position, nbt)
+            VALUES (?, ?, ?)
+            ON CONFLICT(id) DO UPDATE SET
+                position = excluded.position,
+                nbt = excluded.nbt",
+        )
+        .bind(id)
+        .bind(position)
+        .bind(nbt)
+        .execute(&mut **tx)
+        .await?;
+    }
+    Ok(true)
+}
+
+pub(super) async fn server_revision(state: &State) -> crate::Result<i64> {
+    Ok(sqlx::query_scalar::<_, i64>(
+        "SELECT revision
+        FROM synced_server_state
+        WHERE singleton = 1",
+    )
+    .fetch_optional(&state.pool)
+    .await?
+    .unwrap_or(0))
+}
+
+pub(super) async fn load_local(
+    instance_id: &str,
+    state: &State,
+) -> crate::Result<Vec<LocalServer>> {
+    load_local_with(instance_id, &state.pool).await
+}
+
+async fn load_local_with<'e>(
+    instance_id: &str,
+    executor: impl Executor<'e, Database = Sqlite>,
+) -> crate::Result<Vec<LocalServer>> {
+    let rows = sqlx::query(
+        "SELECT id, source, excluded_synced_server_id, nbt, position
+        FROM instance_servers
+        WHERE instance_id = ?
+        ORDER BY position",
+    )
+    .bind(instance_id)
+    .fetch_all(executor)
+    .await?;
+    use sqlx::Row;
+    rows.into_iter()
+        .map(|row| {
+            let id: String = row.get("id");
+            let source: String = row.get("source");
+            let excluded_synced_server_id: Option<String> =
+                row.get("excluded_synced_server_id");
+            let nbt: Vec<u8> = row.get("nbt");
+            let position: i64 = row.get("position");
+            Ok(LocalServer {
+                id,
+                source: ServerSource::from_str(&source).ok_or_else(
+                    || {
+                        ErrorKind::InputError(format!(
+                            "Unknown server source {source}"
+                        ))
+                    },
+                )?,
+                excluded_synced_server_id,
+                data: nbt_from_bytes(nbt)?,
+                position,
+            })
+        })
+        .collect()
+}
+
+pub(super) async fn write_local(
+    instance_id: &str,
+    servers: &[LocalServer],
+    state: &State,
+) -> crate::Result<()> {
+    commit_server_state(None, Some((instance_id, servers)), state).await?;
+    Ok(())
+}
+
+pub(super) async fn write_local_rows(
+    tx: &mut Transaction<'_, Sqlite>,
+    instance_id: &str,
+    servers: &[LocalServer],
+) -> crate::Result<()> {
+    sqlx::query("DELETE FROM instance_servers WHERE instance_id = ?")
+        .bind(instance_id)
+        .execute(&mut **tx)
+        .await?;
+    for server in servers {
+        let source = server.source.as_str();
+        let nbt = nbt_to_bytes(&server.data)?;
+        sqlx::query(
+            "INSERT INTO instance_servers
+                (instance_id, id, source, excluded_synced_server_id,
+                 nbt, position)
+            VALUES (?, ?, ?,
+                (SELECT id FROM synced_servers WHERE id = ?), ?, ?)",
+        )
+        .bind(instance_id)
+        .bind(&server.id)
+        .bind(source)
+        .bind(&server.excluded_synced_server_id)
+        .bind(nbt)
+        .bind(server.position)
+        .execute(&mut **tx)
+        .await?;
+    }
+    Ok(())
+}
+
+pub(super) async fn load_projection_entries(
+    instance_id: &str,
+    state: &State,
+) -> crate::Result<Vec<ProjectionEntry>> {
+    let rows = sqlx::query(
+        "SELECT server_id, owner, nbt, position
+        FROM instance_server_projection_entries
+        WHERE instance_id = ?
+        ORDER BY position",
+    )
+    .bind(instance_id)
+    .fetch_all(&state.pool)
+    .await?;
+    use sqlx::Row;
+    rows.into_iter()
+        .map(|row| {
+            let server_id: String = row.get("server_id");
+            let owner: String = row.get("owner");
+            let nbt: Vec<u8> = row.get("nbt");
+            let position: i64 = row.get("position");
+            Ok(ProjectionEntry {
+                id: server_id,
+                owner: ProjectionOwner::from_str(&owner).ok_or_else(
+                    || {
+                        ErrorKind::InputError(format!(
+                            "Unknown server projection owner {owner}"
+                        ))
+                    },
+                )?,
+                data: nbt_from_bytes(nbt)?,
+                position,
+            })
+        })
+        .collect()
+}
+
+pub(super) async fn begin_server_checkpoint(
+    instance_id: &str,
+    servers: &[ServerRecord],
+    expected_sha1: &str,
+    source_revision: i64,
+    state: &State,
+) -> crate::Result<()> {
+    let mut tx = state.pool.begin().await?;
+    sqlx::query(
+        "DELETE FROM instance_server_projection_entries WHERE instance_id = ?",
+    )
+    .bind(instance_id)
+    .execute(&mut *tx)
+    .await?;
+    for (position, server) in servers.iter().enumerate() {
+        let owner = if server.source == ServerSource::UserSynced {
+            ProjectionOwner::Synced
+        } else {
+            ProjectionOwner::Instance
+        }
+        .as_str();
+        let nbt = nbt_to_bytes(&server.data)?;
+        let position = position as i64;
+        sqlx::query(
+            "INSERT INTO instance_server_projection_entries
+                (instance_id, owner, server_id, nbt, position)
+            VALUES (?, ?, ?, ?, ?)",
+        )
+        .bind(instance_id)
+        .bind(owner)
+        .bind(&server.id)
+        .bind(nbt)
+        .bind(position)
+        .execute(&mut *tx)
+        .await?;
+    }
+    sqlx::query(
+        "INSERT INTO instance_sync_checkpoints
+            (instance_id, feature, variant, expected_sha1, merge_base,
+             source_revision, status, link_mode)
+        VALUES (?, 'multiplayer_servers', 'default', ?, NULL, ?,
+            'pending', NULL)
+        ON CONFLICT(instance_id, feature, variant) DO UPDATE SET
+            expected_sha1 = excluded.expected_sha1,
+            merge_base = NULL,
+            source_revision = excluded.source_revision,
+            status = 'pending',
+            link_mode = NULL",
+    )
+    .bind(instance_id)
+    .bind(expected_sha1)
+    .bind(source_revision)
+    .execute(&mut *tx)
+    .await?;
+    tx.commit().await?;
+    Ok(())
+}
+
+pub(super) fn generated_path(state: &State, instance_id: &str) -> PathBuf {
+    synced_options_path(state)
+        .join("servers/generated")
+        .join(safe_instance_id(instance_id))
+        .join(SERVERS_FILE)
+}
@@ -0,0 +1,131 @@
+use quartz_nbt::NbtCompound;
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum ServerSource {
+    UserSynced,
+    Modpack,
+    LinkedServerProject,
+    LocalDesynced,
+}
+
+impl ServerSource {
+    pub(super) fn as_str(self) -> &'static str {
+        match self {
+            Self::UserSynced => "user_synced",
+            Self::Modpack => "modpack",
+            Self::LinkedServerProject => "linked_server_project",
+            Self::LocalDesynced => "local_desynced",
+        }
+    }
+
+    pub(super) fn from_str(value: &str) -> Option<Self> {
+        match value {
+            "user_synced" => Some(Self::UserSynced),
+            "modpack" => Some(Self::Modpack),
+            "linked_server_project" => Some(Self::LinkedServerProject),
+            "local_desynced" => Some(Self::LocalDesynced),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum DesyncServerMode {
+    KeepInOtherInstances,
+    RemoveFromOtherInstances,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct SyncedServer {
+    pub id: String,
+    pub name: String,
+    pub address: String,
+    pub accept_textures: Option<bool>,
+}
+
+#[derive(Clone, Debug)]
+pub(crate) struct ServerRecord {
+    pub id: String,
+    pub source: ServerSource,
+    pub data: NbtCompound,
+}
+
+impl ServerRecord {
+    pub fn name(&self) -> String {
+        self.data
+            .get::<_, &str>("name")
+            .unwrap_or_default()
+            .to_string()
+    }
+
+    pub fn address(&self) -> String {
+        self.data
+            .get::<_, &str>("ip")
+            .unwrap_or_default()
+            .to_string()
+    }
+
+    pub fn icon(&self) -> Option<String> {
+        self.data.get::<_, &str>("icon").ok().map(ToOwned::to_owned)
+    }
+
+    pub fn hidden(&self) -> bool {
+        self.data.get::<_, i8>("hidden").unwrap_or(0) != 0
+    }
+
+    pub fn accept_textures(&self) -> Option<bool> {
+        self.data
+            .get::<_, i8>("acceptTextures")
+            .ok()
+            .map(|value| value != 0)
+    }
+}
+
+#[derive(Clone)]
+pub(super) struct CanonicalServer {
+    pub id: String,
+    pub data: NbtCompound,
+}
+
+#[derive(Clone)]
+pub(super) struct LocalServer {
+    pub id: String,
+    pub source: ServerSource,
+    pub excluded_synced_server_id: Option<String>,
+    pub data: NbtCompound,
+    pub position: i64,
+}
+
+#[derive(Clone)]
+pub(super) struct ProjectionEntry {
+    pub id: String,
+    pub owner: ProjectionOwner,
+    pub data: NbtCompound,
+    pub position: i64,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub(super) enum ProjectionOwner {
+    Synced,
+    Instance,
+}
+
+impl ProjectionOwner {
+    pub(super) fn as_str(self) -> &'static str {
+        match self {
+            Self::Synced => "synced",
+            Self::Instance => "instance",
+        }
+    }
+
+    pub(super) fn from_str(value: &str) -> Option<Self> {
+        match value {
+            "synced" => Some(Self::Synced),
+            "instance" => Some(Self::Instance),
+            _ => None,
+        }
+    }
+}
@@ -47,6 +47,21 @@ use tokio::io::AsyncReadExt;
 use tokio::process::Command;
 use tokio_util::sync::CancellationToken;

+pub(crate) struct GameVersionMetadata {
+    pub world_version: Option<u32>,
+}
+
+/// Reads the embedded `version.json` DataVersion from a client jar.
+///
+/// Ported as a stub to match the upstream Axolotl implementation, which also
+/// returns `None`; callers fall back to the legacy data-version table.
+pub(crate) async fn read_game_version_metadata_from_jar(
+    _path: &Path,
+) -> crate::Result<Option<GameVersionMetadata>> {
+    Ok(None)
+}
+
+
 #[cfg(target_os = "windows")]
 use winreg::{RegKey, enums::HKEY_CURRENT_USER};

@@ -68,10 +68,17 @@ impl DirectoryInfo {

    /// Get the Minecraft instance metadata directory
    #[inline]
+
    pub fn metadata_dir(&self) -> PathBuf {
        self.config_dir.join(METADATA_FOLDER_NAME)
    }

+    /// Get the directory containing launcher-wide synced option files.
+    #[inline]
+    pub(crate) fn synced_options_dir(&self) -> PathBuf {
+        self.config_dir.join("synced-options")
+    }
+
    /// Get the Minecraft java versions metadata directory
    #[inline]
    pub fn java_versions_dir(&self) -> PathBuf {
@@ -0,0 +1,68 @@
+use super::{CanonicalValue, GameOptionKind, StoredOption, StoredPreference};
+use sqlx::{Row, SqlitePool};
+use std::collections::HashMap;
+
+pub(crate) async fn shared_game_options_exist(
+    pool: &SqlitePool,
+) -> crate::Result<bool> {
+    Ok(sqlx::query_scalar("SELECT EXISTS(SELECT 1 FROM synced_game_option_state WHERE singleton = 1)").fetch_one(pool).await?)
+}
+
+pub(crate) async fn game_options_sync_is_enabled(
+    pool: &SqlitePool,
+) -> crate::Result<bool> {
+    Ok(sqlx::query_scalar("SELECT globally_enabled FROM sync_feature_settings WHERE feature = 'game_options'").fetch_optional(pool).await?.unwrap_or(false))
+}
+
+pub(crate) async fn load_game_options_sync_state(
+    pool: &SqlitePool,
+    current_catalog_revision: u32,
+) -> crate::Result<(u64, u32)> {
+    let row = sqlx::query("SELECT revision, catalog_revision FROM synced_game_option_state WHERE singleton = 1").fetch_optional(pool).await?;
+    Ok(row
+        .map(|r| {
+            (
+                r.get::<i64, _>("revision").max(0) as u64,
+                (r.get::<i64, _>("catalog_revision").max(1) as u32)
+                    .max(current_catalog_revision),
+            )
+        })
+        .unwrap_or((0, current_catalog_revision)))
+}
+
+pub(crate) async fn load_shared_game_options(
+    pool: &SqlitePool,
+) -> crate::Result<HashMap<String, StoredOption>> {
+    let rows = sqlx::query("SELECT option_id, kind, raw_key, canonical_value_json, seeded, revision FROM synced_game_option_values").fetch_all(pool).await?;
+    let mut out = HashMap::with_capacity(rows.len());
+    for row in rows {
+        let option_id: String = row.get("option_id");
+        let kind: String = row.get("kind");
+        let raw_key: Option<String> = row.try_get("raw_key")?;
+        let json: Option<String> = row.try_get("canonical_value_json")?;
+        let seeded: bool = row.get("seeded");
+        let revision: i64 = row.get("revision");
+        out.insert(
+            option_id.clone(),
+            StoredOption {
+                option_id,
+                kind: if kind == "external" {
+                    GameOptionKind::External
+                } else {
+                    GameOptionKind::Vanilla
+                },
+                raw_key,
+                value: json.as_deref().map(serde_json::from_str).transpose()?,
+                seeded,
+                revision: revision.max(0) as u64,
+            },
+        );
+    }
+    Ok(out)
+}
+
+pub(crate) async fn load_game_option_preferences(
+    pool: &SqlitePool,
+) -> crate::Result<HashMap<String, StoredPreference>> {
+    Ok(sqlx::query("SELECT option_id, enabled, revision FROM synced_game_option_preferences").fetch_all(pool).await?.into_iter().map(|r| { let option_id: String = r.get("option_id"); let enabled: bool = r.get("enabled"); let revision: i64 = r.get("revision"); (option_id, StoredPreference { enabled, revision: revision.max(0) as u64 }) }).collect())
+}
@@ -0,0 +1,52 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type", content = "value", rename_all = "snake_case")]
+pub enum CanonicalValue {
+    Bool(bool),
+    Integer(i64),
+    Decimal(String),
+    Enum(String),
+    Text(String),
+    StringList(Vec<String>),
+    KeyBinding(String),
+    ExternalRaw(String),
+}
+
+impl CanonicalValue {
+    pub(crate) fn type_name(&self) -> &'static str {
+        match self {
+            Self::Bool(_) => "bool",
+            Self::Integer(_) => "integer",
+            Self::Decimal(_) => "decimal",
+            Self::Enum(_) => "enum",
+            Self::Text(_) => "text",
+            Self::StringList(_) => "string_list",
+            Self::KeyBinding(_) => "key_binding",
+            Self::ExternalRaw(_) => "external_raw",
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum GameOptionKind {
+    Vanilla,
+    External,
+}
+
+#[derive(Clone)]
+pub(crate) struct StoredOption {
+    pub(crate) option_id: String,
+    pub(crate) kind: GameOptionKind,
+    pub(crate) raw_key: Option<String>,
+    pub(crate) value: Option<CanonicalValue>,
+    pub(crate) seeded: bool,
+    pub(crate) revision: u64,
+}
+
+#[derive(Clone)]
+pub(crate) struct StoredPreference {
+    pub(crate) enabled: bool,
+    pub(crate) revision: u64,
+}
@@ -109,3 +109,47 @@ pub struct InstanceSyncedOptions {
    #[serde(default)]
    pub data_packs: bool,
 }
+
+
+/// The set of per-instance synchronization features. Mirrors the Axolotl
+/// `SyncedOption` enum, including its string keys used by the
+/// `instance_sync_preferences` / `sync_feature_settings` tables.
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum SyncedOption {
+    GameOptions,
+    CommandHistory,
+    MultiplayerServers,
+    CreativeHotbars,
+    Screenshots,
+    ResourcePacks,
+    DataPacks,
+}
+
+impl SyncedOption {
+    pub const ALL: [Self; 7] = [
+        Self::GameOptions,
+        Self::CommandHistory,
+        Self::MultiplayerServers,
+        Self::CreativeHotbars,
+        Self::Screenshots,
+        Self::ResourcePacks,
+        Self::DataPacks,
+    ];
+
+    pub const fn is_available(self) -> bool {
+        true
+    }
+
+    pub const fn as_str(self) -> &'static str {
+        match self {
+            Self::GameOptions => "game_options",
+            Self::CommandHistory => "command_history",
+            Self::MultiplayerServers => "multiplayer_servers",
+            Self::CreativeHotbars => "creative_hotbars",
+            Self::Screenshots => "screenshots",
+            Self::ResourcePacks => "resource_packs",
+            Self::DataPacks => "data_packs",
+        }
+    }
+}
@@ -65,3 +65,5 @@ pub use self::update_check::*;
 fn unknown_value(kind: &str, value: &str) -> crate::Error {
    crate::ErrorKind::InputError(format!("Unknown {kind} {value}")).into()
 }
+mod game_options;
+pub use self::game_options::*;
@@ -67,6 +67,9 @@ pub use self::mr_auth::*;

 mod legacy_converter;

+mod game_options;
+pub use self::game_options::*;
+
 pub mod attached_world_data;
 pub mod server_join_log;

@@ -148,6 +151,9 @@ pub struct State {
    configured_http_client_update: AsyncMutex<()>,

    pub(crate) file_watcher: FileWatcher,
+
+    pub(crate) synced_options_lock: Arc<AsyncMutex<()>>,
+    pub(crate) game_locale_indexer: crate::api::instance::synced_options::game_options::locales::GameLocaleIndexer,
 }

 #[derive(Default)]
@@ -555,6 +561,12 @@ impl State {
        ))
    }

+    pub(crate) async fn lock_synced_options(
+        &self,
+    ) -> tokio::sync::OwnedMutexGuard<()> {
+        self.synced_options_lock.clone().lock_owned().await
+    }
+
    pub fn initialized() -> bool {
        LAUNCHER_STATE.initialized()
    }
@@ -969,6 +981,13 @@ impl State {
    }
 }

+pub(crate) async fn instance_has_running_process(
+    instance_id: &str,
+    state: &State,
+) -> crate::Result<bool> {
+    Ok(state.process_manager.has_instance_process(instance_id))
+}
+
 #[cfg(test)]
 pub(crate) async fn test_state(
    directories: DirectoryInfo,
@@ -1016,6 +1035,8 @@ pub(crate) async fn test_state(
        configured_http_client: RwLock::new(configured_http_client),
        configured_http_client_update: AsyncMutex::new(()),
        file_watcher,
+        synced_options_lock: Arc::new(AsyncMutex::new(())),
+        game_locale_indexer: Default::default(),
    }))
 }