feat(vibe): reconcile mutable session previews in playback

frontend/src/store/useVibeStore.ts

@@ -1,30 +1,34 @@
 import { create } from 'zustand';
 import type { Track, VibeSession } from '../types';
+import type { VibePlanItem } from '../services/vibeService';
 
-// V2 recommendation session state. The backend stores the plan in Redis
-// (keyed by sessionId) and serves tracks one at a time via GET /v2/vibe/next.
-// We keep a lookahead buffer of upcoming Track[] to feed playback.
+// The durable plan is authoritative. `buffer` is only its currently
+// uncommitted, hydrated preview; it may be replaced at any feedback boundary.
 interface VibeState {
   activeSessionId: string | null;
   seedTrackId: string | null;
+  planVersion: number | null;
+  /** Durable cursor for the track currently in Vibe playback. */
+  currentPlanItem: VibePlanItem | null;
   centerTrack: Track | null;
-  buffer: Track[]; // lookahead buffer of upcoming recommended tracks
-  /** Outcome of the first V2 batch, including sessions initiated from Discover. */
+  buffer: Track[];
   initialBatchStatus: 'idle' | 'loading' | 'exhausted' | 'failed';
 
   setActiveSession: (session: VibeSession | null) => void;
   setSeedTrackId: (seedTrackId: string | null) => void;
   setCenterTrack: (track: Track | null) => void;
-  setBuffer: (buffer: Track[]) => void;
+  /** Returns false when a response belongs to an older plan revision. */
+  setPlan: (planVersion: number | null, preview: Track[]) => boolean;
+  setCurrentPlanItem: (item: VibePlanItem | null) => void;
   setInitialBatchStatus: (status: VibeState['initialBatchStatus']) => void;
-  appendBuffer: (tracks: Track[]) => void;
-  shiftBuffer: () => Track | undefined;
   reset: () => void;
 }
 
 const initialState = {
   activeSessionId: null as string | null,
   seedTrackId: null as string | null,
+  planVersion: null as number | null,
+  currentPlanItem: null as VibePlanItem | null,
   centerTrack: null as Track | null,
   buffer: [] as Track[],
   initialBatchStatus: 'idle' as const,
@@ -33,26 +37,20 @@ const initialState = {
 export const useVibeStore = create<VibeState>((set, get) => ({
   ...initialState,
 
-  setActiveSession: (session) =>
-    set(
-      session
-        ? { activeSessionId: session.sessionId, seedTrackId: session.seedTrackId }
-        : { activeSessionId: null, seedTrackId: null }
-    ),
-
+  setActiveSession: (session) => set(
+    session
+      ? { activeSessionId: session.sessionId, seedTrackId: session.seedTrackId }
+      : { activeSessionId: null, seedTrackId: null },
+  ),
   setSeedTrackId: (seedTrackId) => set({ seedTrackId }),
   setCenterTrack: (centerTrack) => set({ centerTrack }),
-  setBuffer: (buffer) => set({ buffer }),
-  setInitialBatchStatus: (initialBatchStatus) => set({ initialBatchStatus }),
-  appendBuffer: (tracks) => set((state) => ({ buffer: [...state.buffer, ...tracks] })),
-
-  shiftBuffer: () => {
-    const { buffer } = get();
-    if (buffer.length === 0) return undefined;
-    const [head, ...rest] = buffer;
-    set({ buffer: rest });
-    return head;
+  setPlan: (planVersion, buffer) => {
+    const current = get().planVersion;
+    if (planVersion === null || (current !== null && planVersion < current)) return false;
+    set({ planVersion, buffer });
+    return true;
   },
-
+  setCurrentPlanItem: (currentPlanItem) => set({ currentPlanItem }),
+  setInitialBatchStatus: (initialBatchStatus) => set({ initialBatchStatus }),
   reset: () => set({ ...initialState }),
 }));