feat(vibe): reconcile mutable session previews in playback

backend/src/services/vibe-session-coordinator.service.test.ts

@@ -47,6 +47,7 @@ function setup() {
     endVibeSessionWithEvent: vi.fn().mockResolvedValue({ session: session('ended'), ended: true }),
     resumeVibeSession: vi.fn().mockResolvedValue({ session: session(), resumed: true }),
     serveNextVibePlanItem: vi.fn().mockResolvedValue({ item: plan().items[0], stale: false }),
+    advancePastUnplayableVibePlanItem: vi.fn().mockResolvedValue({ item: plan().items[0], stale: false }),
     persistNextVibePlan: vi.fn().mockResolvedValue({ ...plan(), version: 2, reason: 'feedback:completed' }),
     getVibePlanForFeedbackEvent: vi.fn().mockResolvedValue(null),
   } as unknown as DbService;
@@ -179,6 +180,25 @@ describe('VibeSessionCoordinator', () => {
     expect(result).toMatchObject({ planVersion: 1, now: { track_id: TRACK_ID } });
   });
 
+  it('advances past an unplayable served item using a distinct idempotent event protocol', async () => {
+    const { db, coordinator } = setup();
+    const planVersionId = '44444444-4444-4444-8444-444444444444';
+    const eventId = '55555555-5555-4555-8555-555555555555';
+
+    const result = await coordinator.advancePastUnplayable('user-1', SESSION_ID, {
+      expectedPlanVersion: 1,
+      planVersionId,
+      ordinal: 0,
+      trackId: TRACK_ID,
+      eventId,
+    });
+
+    expect(db.advancePastUnplayableVibePlanItem).toHaveBeenCalledWith(SESSION_ID, 'user-1', {
+      expectedPlanVersion: 1, planVersionId, ordinal: 0, trackId: TRACK_ID, eventId,
+    });
+    expect(result.now).toMatchObject({ track_id: TRACK_ID });
+  });
+
   it('ends an active session once and preserves its latest persisted plan', async () => {
     const { db, coordinator } = setup();
     const response = await coordinator.end('user-1', SESSION_ID);