Rust backend

The backend lives in tauri/src-tauri/src/. It’s a single long-lived process that owns all state and side effects. This page is a map of the modules.

Foundation

• main.rs / lib.rs — entry point, module wiring, Tauri command registration. The generate_handler! list is the source of truth for every IPC command. Also sets up per-concern State<T>, the single-instance plugin, the tray icon + menu, lifecycle hooks, and CLI dispatch.
• error.rs — AppError enum + AppResult alias, serialisable so errors round-trip across the IPC boundary as strings.
• paths.rs — centralised filesystem path resolution. Every module that touches an app file goes through here.
• cli.rs — argv parsing for headless subcommands (--run, --backup, --release-lock) vs a normal launch.

Persistence

• config.rs — app-wide settings persisted to config.json. The cloud / LAN / Proton-launch fields are grouped into CloudConfig / LanConfig / LaunchConfig sub-structs, #[serde(flatten)]ed so the JSON stays flat. A container-level #[serde(default)] on each config struct means missing keys fall back to the struct’s Default, so older files load without migration (apply it at the struct level, not per-field). Unused fields are removed, not retained for legacy compatibility.
• library.rs — GameEntry + Library CRUD with atomic JSON saves to library.json. Emits library:changed on every mutation.

External integrations

• ludusavi.rs — subprocess invocation of the bundled ludusavi CLI. Owns the manifest cache and the search/find/enrich + restore/backup flow.
• ludusavi_config.rs — Spool owns ludusavi’s config.yaml so it controls backup/restore paths, the cloud remote, retention, and per-restore redirects.
• steamgriddb.rs — HTTP client for SteamGridDB. Downloads portrait covers and extracts a vibrant accent colour.
• steam.rs — non-Steam shortcut creation (shortcuts.vdf) + grid art.
• sync.rs — sync-server HTTP client (the Hono server in server/): account registration, per-game play-state locks, save events, playtime sync.
• metadata.rs — HTTP client for the public Steam Store appdetails API. Enriches game entries with description, developer, publisher, genres, and release date (no API key required).
• lan/ — the LAN game-sharing subsystem (discovery.rs UDP-broadcast peer discovery, server.rs in-process axum file server with blake3 manifests, install.rs the resumable content-addressed receiver).

Platform-specific

These are #[cfg]-gated and degrade gracefully on the other OS.

• Windows-only — launcher.rs (embedded launcher_stub.exe generation), registry.rs (RUNASADMIN probe), process.rs (the elevated run-as-admin path; the normal spawn path is cross-platform).
• Linux-only — proton.rs (umu-launcher + per-game Wine prefixes), gamemode.rs (SteamOS Game Mode detection), session.rs (Game-Mode session records), decky_install.rs (companion Decky plugin installer), redirects.rs (cross-platform save-path mapping), plugin_server.rs (Unix-socket HTTP server for Decky companion communication), suspend.rs (D-Bus system suspend/resume watcher for play locks).

Cross-platform OS integration

• system_open.rs — native “Open folder” with the AppImage env stripped.
• diagnostics.rs — the Settings → Compatibility dependency doctor.

Workflow orchestration

• runner.rs — the marquee feature. A five-phase state machine (restoring → launching → playing → backing-up → done) emitting run:phase events at each transition. A single-launch RAII guard releases the slot even on panic.

Startup backfills

One-shot tasks at boot for legacy library entries, saved once at the end:

• accent_backfill.rs — fills missing accent colours from covers on disk.
• size_backfill.rs — computes install sizes via walkdir.
• metadata_backfill.rs — throttled startup task that enriches library entries having a Steam ID but missing description/developer fields.