Backend Reference

The Rust backend lives in src-tauri/src/. It follows a strict layering rule: Tauri command handlers in commands/ are thin adapters — they validate input, call the service layer, and serialize the result. Business logic belongs in services/.

Streaming Pipeline (Deep Dive)

This is the most complex part of the backend. Understanding it is essential before touching chat, tool calls, or thinking block handling.

Flow

Think Tag Detection

The <think> tag can be split across NDJSON chunk boundaries (e.g. <thi in one chunk, nk> in the next). streaming.rs maintains a small string buffer to handle cross-chunk boundaries. Do not use a single-pass regex for this — it will miss split tags under load.

Tool Call Parsing

Tool calls arrive as <tool_call name="..." arguments="{...}"> in the token stream. Parsing extracts the name attribute and the JSON arguments attribute using secondary regex calls (not a single complex regex — SonarCloud enforces regex complexity < 20).

Command Registry

All 36 Tauri commands are registered in src-tauri/src/lib.rs. To add a new command:

1. Implement the handler in the appropriate file under commands/.
2. Annotate with #[tauri::command].
3. Add it to the generate_handler![] macro call in lib.rs.
4. Add the corresponding invoke() call in the frontend TypeScript.

SQLite Schema

The database is initialised from a single baseline migration at src-tauri/src/db/migrations/001_init_v1.sql. There is no migration runner — the schema is applied once on first launch. See src-tauri/src/db/ for per-table modules.

Key tables: conversations, messages, hosts, settings, model_user_data (tags, favorites, per-model defaults).

AppState

src-tauri/src/state.rs defines AppState, shared across all commands via Tauri's managed state:

pub struct AppState {
    pub db: DbConn,          // Arc<Mutex<Connection>>
    pub client: reqwest::Client,
    pub cancel_tx: Option<CancelSender>,
    pub health_handles: HealthHandles,
}

Access it in a command with state: tauri::State<'_, AppState>.