Decision: The backend is split into folders by role, and main.rs only wires things up

Context

The backend (src-tauri/src) was 16 flat modules, and main.rs alone was 919 lines holding app state, command dispatch, the tray, file opening and startup wiring. The names were confusing too. cli.rs was the Claude and Codex CLIs used for chat, while agentcli.rs was the app's own CLI mode. Finding a place for a new feature meant opening several files.

Decision

We split the backend into folders by role.

Place	Job
main.rs	Startup wiring only
app.rs	App state, loading and saving, telling every window about changes
commands.rs	Commands the page can call
chat/	Chat, AI connections (subscription CLIs, HTTP), prompts
pets/	Pet files, importing from an address, friends in the yard
agent/	The app's CLI mode (hooks, MCP) and the local bridge
desktop/	The desktop overlay and strolling
i18n/	The backend strings table
window.rs, tray.rs, system.rs, store.rs, update.rs	Windows, tray, opening with the OS, file storage, auto-update

The scripts that build distribution files follow the same rule and live in packaging/{macos,linux,windows} (the old ci/ was not CI but local distribution builds).

Consequences

• Positive: File names say what the file does. main.rs is now 114 lines. The guard tests no longer keep a hand-written file list; they scan all of src/, so new modules are checked automatically.
• Negative: Files moved, so following git history needs git log --follow. Paths between modules got longer (crate::chat::providers).
• Neutral: Folders go one level deep at most. Splitting further is decided when a file grows.

Follow-up (2026-10-10)

The same rule has since gone one level further where files grew. app.rs keeps the state, commit, the locks and announcing changes, with loading in app/load.rs and the sprite protocol in app/sprite.rs. commands.rs is one COMMANDS table, a row per command with who may ask for it and what it does, from which the page's bridge, the access check and the dispatch come. main.rs is 186 lines.

Alternatives considered

• Keep the flat layout and only split main.rs: main.rs shrinks, but the cli.rs and agentcli.rs confusion stays.
• Split into crates with a Cargo workspace: Boundaries get stronger, but at this size the build configuration and visibility management cost more than they give.