# OpenCode Mobile — Technical Design Document (TDD)

> Audience: engineers working on the app. For product-level context and user
> stories, see [`prd.md`](./prd.md).

## 1. Stack

| Layer | Choice | Notes |
| ----- | ------ | ----- |
| Runtime | React Native 0.81 + Hermes | New architecture / Fabric on by default via Expo SDK 54 |
| Framework | Expo SDK 54 + Expo Router 6 | File-based routing under `app/`; typed routes enabled |
| State | Zustand 5 | Plain stores, no provider tree. Avoids redux boilerplate. |
| Server data | TanStack Query 5 (cache) + custom `fetch`-based SDK | SSE is hand-rolled (RN's `EventSource` is unreliable). |
| Persistence | `expo-secure-store` (Keychain / Keystore) | All connection URLs + passwords. |
| Auth | `expo-local-authentication` | Optional biometric gate at startup and per-send. |
| Notifications | `expo-notifications` | Local + push; tap deep-links into session. |
| Crash reporting | `@sentry/react-native` 6.x | Opt-in via env DSN; full URL scrubbing in `beforeSend`. |

## 2. Repo Layout

```
app/                       Expo Router screens (file-based routes)
├── _layout.tsx            Root layout: Sentry init, ErrorBoundary, providers, SSE wiring
├── (tabs)/                Bottom tabs: sessions, connections, settings
├── session/[id].tsx       Chat screen
└── connection/            Add / edit connection screens

src/
├── components/
│   ├── ErrorBoundary.tsx  App-wide React error boundary with Share Report fallback
│   ├── AuthGate.tsx       Biometric prompt before app contents render
│   ├── chat/              Message bubbles, tool call cards, etc.
│   └── markdown/          react-native-marked wrapper + custom code-block
├── lib/
│   ├── sdk.ts             HTTP + SSE client for the opencode server API
│   ├── sentry.ts          Sentry wrapper + global JS/promise handlers + scrubbing
│   ├── diagnostics.ts     Active connection probes + crash report builder + share
│   ├── logbuffer.ts       200-line ring buffer mirroring console output
│   ├── notifications.ts   Notification setup + categories + dedupe
│   ├── speech.ts          Voice input via expo-speech-recognition (experimental; PRD §7 lists voice beyond OS dictation as out-of-scope for v0.x)
│   └── types.ts           Re-exported model/connection types
└── stores/
    ├── auth.ts            Biometric state
    ├── connections.ts     Server list, active client, project metadata
    ├── sessions.ts        Session list, messages, parts, optimistic sends
    ├── events.ts          SSE event loop, reconnect, status tracking
    ├── settings.ts        User preferences (notifications, biometrics)
    └── catalog.ts         Models / providers / commands catalog

docs/                      PRD + TDD (this file)
scripts/                   E2E test rig (LLM-driven CUA Android smoke)
```

## 3. Data Flow

```
+--------------+    HTTP    +-----------------+
|  React UI    | ---------> |  src/lib/sdk.ts |
+------+-------+            +--------+--------+
       ^                             |
       |                             | fetch / SSE
       |                             v
+------+-------+            +-----------------+
| Zustand      | <--------- |  opencode srv   |
| stores       |   events   +-----------------+
+--------------+
```

- The UI never calls `fetch` directly. It calls store actions, which call the SDK.
- SSE is owned by `stores/events.ts`. It dispatches events into `sessions.ts`, `connections.ts` and notification helpers — UI components only read derived state.
- Optimistic updates (e.g. `sendMessage`) are rolled back when the server's SSE truth disagrees.

## 4. Connection Lifecycle

1. `loadConnections()` reads stored connections from SecureStore at startup.
2. Active connection (if any) builds a `Client` via `createClient({ baseUrl, directory, auth })`.
3. `client.project.current()` and `client.path.get()` fill in project + server-home metadata; failures are non-fatal (server might be offline). `serverHome` is still consumed by the directory switcher for `~` expansion — but the former *session-scoping* use of this metadata (`sessionScope.ts`, which always resolved to the default client) was dead and removed in `472ff8d`.
4. The `useEffect` in `_layout.tsx` keyed on `client` starts the SSE event loop the moment a client exists, and stops it when the user removes/changes the connection.
5. **Active diagnostics on failure.** When a connection is added or tested and fails, `src/lib/diagnostics.ts:probeConnection` runs three parallel probes (health, server-root, public-internet) and classifies the cause (`tls-error`, `timeout`, `no-internet`, `server-unreachable`, `health-failed`, `malformed-url`, `unknown`). The result drives both the UI alert and the Sentry capture.

## 5. SSE & Reconnect

Implemented in `src/stores/events.ts` (`connect`):

- `AbortController` per connection attempt.
- Async iteration over `client.global.events(signal)`.
- A **stable-connection timer** (`STABLE_CONNECTION_MS = 10s`) resets the reconnect attempt counter once the stream has been alive long enough — this prevents a healthy stream from accumulating false-positive attempt history.
- Backoff: `[1s, 2s, 4s, 8s, 15s]` with ±25 % jitter, capped at 15 s.
- After `PROLONGED_DISCONNECT_MS = 30s` of being down, a notification fires once (deduped with a 60 s cooldown).
- Disconnect clears all in-flight sessionStatus / statusText / permissions / questions — SSE is the source of truth, never local cache.

## 6. Error Handling & Crash Reporting

We treat errors at three layers and route them differently:

| Layer | Mechanism | Sent to Sentry? |
| ----- | --------- | --------------- |
| Expected operational errors (timeout, biometric cancel, network blip) | Caught locally, stored in store `error` field, surfaced as `Alert` / inline UI | **No** — keeps signal high |
| Connection failures (specifically connect/test/add) | `probeConnection()` → `captureDiagnostic()` with classification + probe context | **Yes**, always, when DSN present |
| Unexpected crashes | Global handlers + React `ErrorBoundary` | **Yes**, always, when DSN present |

### 6.1 Sentry init (`src/lib/sentry.ts`)

- DSN comes from `EXPO_PUBLIC_SENTRY_DSN`; if missing, init is a no-op and a breadcrumb-free build is shipped.
- `release` and `dist` are set from `app.json.expo.version` so Sentry can correlate stack traces to source-map artifacts.
- `tracesSampleRate: 0` — performance tracing intentionally off.
- `enableNative: true`, `enableNativeCrashHandling: true` — native (Android NDK / iOS Mach) crashes are captured.
- `maxBreadcrumbs: 100`.
- `beforeSend` and `beforeBreadcrumb` run every outgoing event/breadcrumb through `scrubEvent` / `scrubString` / `scrubObject`. These strip basic-auth (`//user:pw@`) and known query-secret keys (`token`, `access_token`, `api_key`, `key`, `password`, `pwd`, `auth`) from any URL anywhere in the payload (request URL, exception value, breadcrumb data).

### 6.2 Global handlers

Even though `@sentry/react-native` wires its own `ReactNativeErrorHandlers` by default, we install our own thin handlers on top so:

1. The 200-line in-memory log buffer (`logbuffer.ts`) always sees the crash — so the *offline* "Share Report" path includes the stack trace even when telemetry is disabled.
2. Telemetry-disabled builds still leave a forensic trail.

Handlers wrap (not replace) the previous handler:

- `ErrorUtils.setGlobalHandler` — captures uncaught JS exceptions from the RN bridge. Tagged `crash.source=js-global`, `crash.fatal=true|false`.
- `globalThis.onunhandledrejection` — captures unhandled promise rejections. Tagged `crash.source=promise-rejection`.

### 6.3 React Error Boundary (`src/components/ErrorBoundary.tsx`)

A class component because `getDerivedStateFromError` / `componentDidCatch` have no hook equivalent. It:

- Catches render-phase exceptions anywhere in the tree.
- Calls `captureException(err, { level: 'fatal', tags: { 'crash.source': 'react-boundary' }, extra: { componentStack } })`.
- Renders a dark-themed recovery screen with the error message, top 6 stack frames, top 6 component-stack frames, and two buttons:
  - **Share Report** → `buildCrashReport(err, 'react-boundary')` → `shareReport()` (clipboard + native share sheet, fully offline).
  - **Try Again** → resets boundary state, remounting children.
- Wraps the entire app inside `_layout.tsx`, outside `GestureHandlerRootView`. `Sentry.wrap(RootLayout)` remains as a second layer of safety net but is rarely the visible one.

### 6.4 Breadcrumbs

Selective, high-signal — not on every action. Crash reports need *just enough* context to reconstruct what the user was doing:

| Site | Category | Message |
| ---- | -------- | ------- |
| `_layout.tsx` initial load | `app.lifecycle` | `app started` |
| `connections.setActiveConnection` | `connection` | `active connection set: <type>` / `…cleared` |
| `events.connect` | `sse` | `connecting` |
| `events.scheduleReconnect` | `sse` (warning) | `reconnect scheduled` (attempt, delay, reason) |
| `events.disconnect` | `sse` | `disconnected` |
| `sessions.selectSession` | `session` | `select` (sessionID, hasDirectory) |

Adding more breadcrumbs is encouraged when triaging a real bug — just keep them out of hot loops.

### 6.5 Diagnostic report (`src/lib/diagnostics.ts`)

A `DiagnosticReport` is the canonical shape both connection-failure flows and crash flows produce. The same `shareReport()` function copies it to the clipboard and opens the native share sheet, so users see one consistent UI regardless of error source.

`formatReport()` includes: classification, summary, target URL, per-probe results, device info, **and the full log-buffer dump**. That last bit is what makes user-shared reports actionable: we get a 200-line trace of what was happening immediately before the failure.

### 6.6 URL / secret scrubbing

Single source of truth: `scrubUrl(url)` in `sentry.ts`. Applied:

- in `captureDiagnostic` before attaching the URL to the Sentry context;
- in `beforeSend` to recurse over every `event.request.url`, `event.message`, every `exception.value`, every breadcrumb;
- in `beforeBreadcrumb` for breadcrumb data added between events.

A test for this would feed a basic-auth URL into a fake event and assert the scrubbed output. (Not yet written — TODO.)

## 7. Versioning & Releases

- Single source of truth for the human-facing version is `app.json` → `expo.version` (e.g. `0.4.6`). Since v0.4.6 the `package.json` `version` is kept in sync with it (both are bumped together on release); earlier builds left `package.json` untouched.
- Git tag `v<version>` triggers `.github/workflows/build.yml` which builds an APK and creates a GitHub Release.
- Sentry `release` is set to `opencode-mobile@<version>` so source maps (uploaded by `sentry-cli` during build) line up with reported stack frames.

## 8. Style Guide (from AGENTS.md)

- Prefer `const` over `let`.
- Early returns over `else`.
- Single-word variable names where reasonable.
- Avoid `any` — use `unknown` and narrow, or a defined type.
- Avoid `try/catch` where you can use `.catch` at the call site; reserve it for boundary points (init, fetch wrappers, event loops).

## 9. Known Gaps / Tech Debt

- **No automated tests for the error pipeline.** Unit tests for `scrubUrl`, `buildCrashReport`, and the global handlers would catch regressions in the privacy guarantees.
- **No fallback UI for SSE disconnect.** Today the user sees the existing chat with a (small) banner; a more deliberate "Reconnecting…" affordance would help.
- **Silent `.catch(() => null)` in stores.** Intentional today (these are non-critical fetches), but should be revisited once we have proper severity tiers for breadcrumbs.
- **PRD analytics.** No usage analytics; only crash telemetry. A future opt-in product-analytics provider could close that loop without compromising the privacy posture.