Imported from freemansoft/fs-game-score (.claude/skills/fs-game-score-live-sync/SKILL.md). Install upstream with npx skills add freemansoft/fs-game-score --skill fs-game-score-live-sync. Copyright stays with the author.

FS Score Card — Live game sync

View-only LAN score sharing. Host owns real state in gameNotifierProvider / playersNotifierProvider. Spectator mirrors wire snapshots in gameSyncSpectatorProvider — never writes prefs or host notifiers.

Full reference: docs/Game-Sync.md. State overview: State-Management.md — Live score sync.

Always use fvm flutter per CLAUDE.md.

Platform scope (v1)

canHostLiveSync / canJoinLiveSync in lib/sync/game_sync_platform.dart — Android/iOS native only. Web/desktop hide live host/join; CSV share unchanged. Real mDNS E2E needs two devices on the same Wi-Fi; emulators use manual ws:// in kDebugMode on the join screen.

Providers

gameSyncHostProvider (lib/provider/game_sync_host_provider.dart)

• Reads game + players notifiers; does not own game state.
• startHosting() → resolveLiveSyncAppVersion(game) → startGameSyncHost(initialSnapshot, pin, requiredAppVersion).
• Unknown version → errorMessage: 'live_sync_app_version_unknown'.
• Listens to game/players → broadcastCurrentState() (revision++, broadcastGameSyncSnapshot).
• Snapshot hostDeviceName = liveSyncConnectionLabel(gameId:, hostIp:) — short game ID or LAN IP, never Platform.localHostname.
• stopHosting() on dispose, new game, or leaving score table (score_table_screen, new_game_control).

gameSyncSpectatorProvider (lib/provider/game_sync_spectator_provider.dart)

• Owns mirrored Game / Players for read-only UI only.
• gameSyncTransportFactoryProvider → GameSyncTransport Function(). connect() creates a fresh transport each time (never reuse disposed instances).
• connect(wsUrl, pin) → Future<GameSyncConnectResult> — completes on first snapshot, terminal error, or 15s timeout. Sets connectedHostIp from parsed URL.
• isConnected requires connected + non-null game and players (first snapshot received).
• Clears mirrored state on idle, wrongPin, versionMismatch, hostClosed.

Wire protocol

lib/sync/game_sync_protocol.dart — JSON over WebSocket.

Types: hello, welcome, reject, snapshot, ping, pong, hostClosed.

URL / QR: ws://<host-ip>:8765?game=<gameId>&pin=<pin> (game_sync_qr.dart). mDNS: _fsscore._tcp.

Mapper: game_sync_mapper.dart ↔ Game + Players.

Wire compatibility and versioning (check on every change)

The shared snapshot shape is GameConfiguration.toJson() keys/types + Player.toJson() keys/types + the protocol message structure in game_sync_protocol.dart. The compatibility boundary is the major semver: gameSyncAppVersionsMatch admits a spectator only when its major matches the host's (1.12.0+236 ↔ 1.13.0+200 OK; 2.x ↔ 1.x rejected).

Before finishing any change, ask: did the shared snapshot shape change?

• Breaking → bump the MAJOR version (pubspec.yaml, CHANGELOG; see fs-game-score-release-engineer): removing, renaming, or retyping any key in GameConfiguration.toJson / Player.toJson, or changing a protocol message's structure. A same-major spectator would mis-parse, so the major bump is what makes mismatched shapes refuse to connect.
• Non-breaking → no major bump: adding a new value to an existing enum field (e.g. a new GameMode — fromJson falls back to the default for unknown values and same-major peers share the code), or adding an optional key that older readers can ignore.

Adding GameMode values (Golf, Hearts) was non-breaking — new values in the existing gameMode string, shape unchanged. Descriptor-only fields (GameRules: winDirection, endCondition, roundOptions, suggestedMaxRounds) are derived from gameMode and never serialized, so they never affect the wire.

Handshake and validation

1. Spectator sends hello: { pin, appVersion, spectatorName }.
2. Host validates 6-digit PIN → else reject / wrongPin (gameSyncRejectWrongPin).
3. Host validates appVersion via gameSyncAppVersionsMatch (non-empty, same major semver, e.g. 1.12.0+236 matches 1.13.0+200) → else versionMismatch (gameSyncRejectVersionMismatch).
4. Host sends welcome + initial snapshot; later snapshots on each broadcast.
5. Spectator re-checks host version on welcome (defense in depth).
6. JoinLiveGameScreen awaits GameSyncConnectResult.connected before goNamed('live-spectator').

App version: global appVersion from PackageInfo in bootstrapApp(), else GameConfiguration.version via resolveLiveSyncAppVersion() (game_sync_app_version.dart).

Connection banner (spectator)

LiveConnectionBanner + resolveLiveConnectionBannerTarget() (game_sync_connection_label.dart):

1. Short game ID (first 8 chars of spectator.game?.gameId)
2. Else LAN IPv4 from connectedHostIp or snapshot hostDeviceName
3. Else liveConnectionConnectedOnly — never localhost

UI touchpoints

L10n: liveConnectionConnected, liveConnectionConnectedOnly, liveConnectionWrongPin, liveConnectionVersionMismatch, liveSyncAppVersionUnknown.

Debug logging

lib/sync/game_sync_log.dart — gameSyncLog(), gameSyncLogConnectionState() inside assert() (debug builds only).

Testing

See fs-game-score-testing-workflow for integration and fake transport patterns.

Key files

• lib/provider/game_sync_host_provider.dart, lib/provider/game_sync_spectator_provider.dart
• lib/sync/game_sync_lan_io.dart, game_sync_transport.dart, fake_game_sync_transport.dart
• lib/presentation/live_share_control.dart, join_live_game_screen.dart, live_connection_banner.dart