feat: session goals - server-driven goal loop with independent small-model audit (#2148)

Arm the target button in the composer and the next prompt becomes a goal:
the server keeps the session working toward it (idle tick -> small-model
audit -> continuation) until the objective is verifiably complete, blocked,
or out of budget — even with the UI closed.

Server (packages/web/server/lib/session-goal):
- event-driven loop on the global SSE hub; goal state lives in
  session.metadata.openchamber.goal (merge-safe patches, stale-write guard
  by goal id), so it survives restarts and syncs to every client for free
- the small-model audit (objective + last assistant turn only, language
  pinned to the objective) is the sole termination authority; blocked needs
  3 consecutive verdicts, audit outages tolerate one unaudited continuation
  then stop the goal as resumable-blocked
- hard stops: optional token budget, auto-continuation cap (Resume grants a
  fresh allowance), turn errors; user abort pauses the goal instead of
  blocking it, and resuming over an aborted tail nudges immediately
- token accounting as a snapshot of the latest turn (input + cache.read +
  output), goal-relative via a creation baseline and segmented across
  compactions; a compaction summary skips the audit and continues
- continuations reuse the session's own provider/model/agent/variant

UI:
- three-mode target button (arm / disarm / manage dialog), informational
  goal strip with inline pause/resume and an Evaluating indicator, sidebar
  state glyph, objective length counter (2000-char server clamp),
  read-only completed goals
- goal entry points: composer (sessions and drafts), start-new-session-
  from-answer dialog, plan implement dialog (plan content becomes the
  objective), scheduled tasks (Run as goal + budget)
- Settings -> Chat -> Goal: feature toggle + default token budget with
  three-layer parity (web server, client persistence, VS Code bridge);
  VS Code renders goal state but hides the entry points (the loop runs in
  the web server only)

Notifications: per-turn "ready" notifications are suppressed while a goal
is active; settling sends one final notification (desktop, web-push, APNs
generic titles with the session name as body) honoring the completion
toggle. Error/question/permission notifications are untouched.

Docs: user guide (session-goals) in all 9 locales + sidebar entry,
scheduled-tasks cross-reference, server module DOCUMENTATION.md.

packages/web/server/index.js

@@ -73,6 +73,7 @@ import { createBootstrapRuntime } from './lib/opencode/bootstrap-runtime.js';
 import { createSessionRuntime } from './lib/opencode/session-runtime.js';
 import { createOpenCodeWatcherRuntime } from './lib/opencode/watcher.js';
 import { createSessionAssistRuntime } from './lib/session-assist/runtime.js';
+import { createSessionGoalRuntime } from './lib/session-goal/runtime.js';
 import { createScheduledTasksRuntime } from './lib/scheduled-tasks/runtime.js';
 import { createServerStartupRuntime } from './lib/opencode/server-startup-runtime.js';
 import { createTunnelWiringRuntime } from './lib/opencode/tunnel-wiring-runtime.js';
@@ -724,6 +725,46 @@ const sessionAssistRuntime = createSessionAssistRuntime({
   getSmallModelService: async () => import('./lib/small-model/index.js'),
 });
 
+const sessionGoalRuntime = createSessionGoalRuntime({
+  buildOpenCodeUrl,
+  getOpenCodeAuthHeaders,
+  getSmallModelService: async () => import('./lib/small-model/index.js'),
+  emitGoalNotification: async ({ sessionId, directory, status, goal }) => {
+    // The goal settle notification replaces the per-turn ready notifications
+    // (suppressed while the goal is active) — so it obeys the same toggle.
+    const settings = await readSettingsFromDisk();
+    if (settings.notifyOnCompletion === false) {
+      return;
+    }
+    const title = status === 'complete'
+      ? 'Goal complete'
+      : (status === 'budgetLimited' ? 'Goal reached its token budget' : 'Goal blocked');
+    const detail = goal?.statusReason && goal.statusReason !== 'verified by audit' && goal.statusReason !== 'reported by agent'
+      ? goal.statusReason
+      : (goal?.note || '');
+    const objective = typeof goal?.objective === 'string' ? goal.objective.slice(0, 140) : '';
+    const notificationPayload = {
+      title,
+      body: [objective, detail].filter(Boolean).join(' — ').slice(0, 240),
+      tag: `goal-${sessionId}`,
+      kind: 'goal',
+      sessionId,
+      directory,
+    };
+    const desktopNotificationDelivered = emitDesktopNotification(notificationPayload);
+    broadcastUiNotification(notificationPayload, { desktopNotificationDelivered });
+    void notificationTriggerRuntime.sendGoalSettlePush({
+      sessionId,
+      directory,
+      status,
+      title,
+      body: notificationPayload.body,
+    }).catch((error) => {
+      console.warn('[session-goal] push fanout failed:', error?.message || error);
+    });
+  },
+});
+
 const globalMessageStreamHub = createGlobalMessageStreamHub({
   buildOpenCodeUrl,
   getOpenCodeAuthHeaders,
@@ -754,6 +795,7 @@ globalMessageStreamHub.subscribeEvent((event) => {
     ? event.directory
     : '';
   sessionAssistRuntime.processPayload(payload, directory);
+  sessionGoalRuntime.processPayload(payload, directory);
 });
 
 const processForwardedEventPayload = (payload, emitSyntheticEvent) => {
@@ -1070,6 +1112,7 @@ const gracefulShutdownRuntime = createGracefulShutdownRuntime({
   syncToHmrState,
   openCodeWatcherRuntime,
   sessionAssistRuntime,
+  sessionGoalRuntime,
   sessionRuntime,
   getHealthCheckInterval: () => healthCheckInterval,
   clearHealthCheckInterval: (value) => clearInterval(value),