feat(vibe): persist durable session plans and events

backend/src/db/migrations.ts

@@ -644,4 +644,68 @@ export const MIGRATIONS: Migration[] = [
       EXECUTE FUNCTION propagate_album_release_date_to_tracks();
     `,
   },
+  {
+    // Vibe v2 needs an immutable event ledger and revisioned plans. The
+    // legacy session_state table remains in place as a derived-state cache so
+    // existing v2 endpoints can migrate independently.
+    id: '20260801_vibe_session_persistence',
+    sql: `
+      CREATE TABLE IF NOT EXISTS vibe_sessions (
+        id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+        user_id UUID NOT NULL,
+        status TEXT NOT NULL CHECK (status IN ('active', 'paused', 'ended', 'expired', 'replaced')),
+        seed_track_id UUID REFERENCES tracks(id) ON DELETE SET NULL,
+        context JSONB NOT NULL DEFAULT '{}'::jsonb,
+        policy_version TEXT NOT NULL,
+        started_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+        last_event_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+        ended_at TIMESTAMPTZ
+      );
+      CREATE INDEX IF NOT EXISTS idx_vibe_sessions_user_last_event
+        ON vibe_sessions (user_id, last_event_at DESC);
+
+      CREATE TABLE IF NOT EXISTS vibe_events (
+        id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+        client_event_id UUID,
+        session_id UUID NOT NULL REFERENCES vibe_sessions(id) ON DELETE CASCADE,
+        user_id UUID NOT NULL,
+        track_id UUID REFERENCES tracks(id) ON DELETE SET NULL,
+        type TEXT NOT NULL,
+        occurred_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+        position_ms INTEGER,
+        duration_ms INTEGER,
+        payload JSONB NOT NULL DEFAULT '{}'::jsonb,
+        UNIQUE (session_id, client_event_id)
+      );
+      CREATE INDEX IF NOT EXISTS idx_vibe_events_session_occurred
+        ON vibe_events (session_id, occurred_at);
+      CREATE INDEX IF NOT EXISTS idx_vibe_events_user_occurred
+        ON vibe_events (user_id, occurred_at DESC);
+
+      CREATE TABLE IF NOT EXISTS vibe_plan_versions (
+        id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+        session_id UUID NOT NULL REFERENCES vibe_sessions(id) ON DELETE CASCADE,
+        version INTEGER NOT NULL CHECK (version > 0),
+        reason TEXT NOT NULL,
+        state_snapshot JSONB NOT NULL,
+        objective_snapshot JSONB NOT NULL,
+        created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+        UNIQUE (session_id, version)
+      );
+
+      CREATE TABLE IF NOT EXISTS vibe_plan_items (
+        plan_version_id UUID NOT NULL REFERENCES vibe_plan_versions(id) ON DELETE CASCADE,
+        ordinal INTEGER NOT NULL CHECK (ordinal >= 0),
+        track_id UUID NOT NULL REFERENCES tracks(id) ON DELETE CASCADE,
+        slot_role TEXT,
+        candidate_source TEXT NOT NULL,
+        score REAL NOT NULL,
+        score_breakdown JSONB NOT NULL,
+        explanation JSONB NOT NULL,
+        committed BOOLEAN NOT NULL DEFAULT false,
+        PRIMARY KEY (plan_version_id, ordinal),
+        UNIQUE (plan_version_id, track_id)
+      );
+    `,
+  },
 ];