# UI ↔ backend contract

The Svelte UI (`src/`) talks to the Rust backend (`src-tauri/`) only through the
Tauri commands and events below. `src/lib/backend.ts` is the single place that
calls them. When the page runs outside Tauri (a plain browser, for design work),
it falls back to a mock with the same shapes.

All names are snake_case on the wire (serde defaults), and timestamps are Unix seconds.

## Types

```ts
type Phase =
  | "idle"          // nothing running
  | "checking"      // probing the site
  | "signing_in"    // browser sign-in in progress
  | "installing"    // downloading + verifying a version
  | "restoring"     // loading the database snapshot into local Postgres
  | "launching"     // starting Postgres → API → tile server → Odian.exe
  | "running"       // Odian.exe is open
  | "error";        // the last long operation failed; see `error`

interface Status {
  online: boolean;              // the site's update service answered /v1/health
  site: { url: string; name: string | null };
  operator: string | null;      // last signed-in ODIAN username (cached; valid offline)
  signed_in: boolean;           // this PC remembers the operator's site sign-in until Sign out: the
                                // launcher renews the short Engine token by itself (launcher session)
  installed: string | null;     // installed version, e.g. "0.51.0"
  available: string | null;    // the site's CURRENT version (online only)
  update_required: boolean;     // online && installed !== null && available !== null && installed !== available
                                // (never true when nothing is installed: that is a first install)
  can_launch: boolean;          // installed && !update_required && phase is idle or error
  phase: Phase;
  error: string | null;         // set with phase "error"; cleared by the next command or `refresh`
  install_dir: string;          // e.g. "D:\\ODIAN"
}

interface Settings {
  site_url: string;             // e.g. "http://192.168.1.41:30097"
  mcp_url: string;              // site MCP, for Keycloak sign-in
  install_dir: string;
}

interface InstallProgress {
  stage: "manifest" | "app" | "db" | "src" | "tiles" | "restore" | "finalize";
  stage_index: number;          // 1-based
  stage_count: number;
  done_bytes: number;           // within the current stage
  total_bytes: number;          // of the current stage; 0 when unknown
  done_items: number;           // within the current stage
  total_items: number;
  bytes_per_sec: number;
  message: string | null;       // e.g. "tiles dark/protomaps_20260423: 412/1402 blocks"
}

interface StackEvent {
  component: "postgres" | "api" | "tiles" | "odian";
  state: "starting" | "ready" | "stopped" | "failed";
  message: string | null;
}

interface LogEvent { level: "info" | "warn" | "error"; message: string; at: number }
```

## Commands (`invoke`)

| Command | Args | Returns | Notes |
|---|---|---|---|
| `get_status` | — | `Status` | cheap; no network |
| `refresh` | — | `Status` | re-probes the site (2 s timeout); also clears an `error` phase |
| `sign_in` | — | `{ username: string }` | opens the system browser (MCP desktop flow) and waits for the loopback callback. Rejects with "Sign-in was cancelled." after `cancel_sign_in` (phase returns to idle, not error). |
| `cancel_sign_in` | — | `void` | abandons a sign-in that is waiting for the browser |
| `sign_out` | — | `Status` | forgets the operator on this PC: the site sign-in, its launcher session (ended on the site when reachable) and the cached operator. **Offline launch needs a new sign-in afterwards**, so the UI confirms first |
| `get_notes` | `{ version?: string }` | `string` | Markdown. From the site when online; the cached copy of the installed version offline. **Untrusted: the UI must sanitize.** |
| `open_external` | `{ url: string }` | `void` | opens an `http`/`https` link in the system browser (links in patch notes); anything else is refused |
| `start_install` | — | `void` | installs or updates to `available`; needs `signed_in` (the site checks the token); progress arrives as events |
| `start_install_from_drive` | `{ path: string }` | `void` | same, reading an ODIAN drive (SSD) instead of the site; no sign-in needed |
| `cancel_install` | — | `void` | stops at the next file boundary; everything already verified is kept |
| `launch` | — | `void` | starts the local stack; `stack` events follow |
| `stop` | — | `void` | stops Odian.exe's stack cleanly |
| `get_stack` | — | `StackEvent[]` | the latest event per component of the current or last launch (for a reloaded UI) |
| `get_settings` | — | `Settings` | |
| `set_settings` | `{ settings: Settings }` | `Status` | |
| `pick_folder` | — | `string \| null` | native folder picker |

Errors reject the promise with a string message.

Planned, not yet available: the size of `available` for the Install button, and
inspecting a drive (its version and size) before installing from it.

## Events (`listen`)

| Event | Payload | When |
|---|---|---|
| `status` | `Status` | whenever any field changes |
| `install-progress` | `InstallProgress` | at most ~10 per second while installing |
| `stack` | `StackEvent` | on each component state change |
| `log` | `LogEvent` | notable backend messages, for the activity panel |