feat(vibe): adapt sessions to context and exploration

backend/src/db/migrations.ts

@@ -720,4 +720,43 @@ export const MIGRATIONS: Migration[] = [
       );
     `,
   },
+  {
+    // Session-specific exploration, goals, and deliberately lossy session
+    // fingerprints are derived from the immutable Vibe ledger. Keeping them
+    // separate from listener_beliefs prevents a transient session from
+    // rewriting permanent taste.
+    id: '20260802_vibe_context_memory_exploration',
+    sql: `
+      CREATE TABLE IF NOT EXISTS vibe_session_profiles (
+        session_id UUID PRIMARY KEY REFERENCES vibe_sessions(id) ON DELETE CASCADE,
+        user_id UUID NOT NULL,
+        fingerprint JSONB NOT NULL DEFAULT '{}'::jsonb,
+        goals JSONB NOT NULL DEFAULT '{"type":"discovery","target":1,"progress":0}'::jsonb,
+        exploration_coefficient REAL NOT NULL DEFAULT 0.30
+          CHECK (exploration_coefficient >= 0 AND exploration_coefficient <= 1),
+        discovery_radius REAL NOT NULL DEFAULT 0.38
+          CHECK (discovery_radius >= 0 AND discovery_radius <= 1),
+        updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+      );
+      CREATE INDEX IF NOT EXISTS idx_vibe_session_profiles_user_updated
+        ON vibe_session_profiles (user_id, updated_at DESC);
+
+      CREATE TABLE IF NOT EXISTS vibe_session_feedback_projections (
+        event_id UUID PRIMARY KEY REFERENCES vibe_events(id) ON DELETE CASCADE,
+        projected_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+      );
+    `,
+  },
+  {
+    // The profile table was introduced after durable sessions. Backfill every
+    // pre-existing session before feedback can claim its exactly-once marker;
+    // newly created sessions receive their context-derived initial goals in
+    // createVibeSession's transaction.
+    id: '20260802_vibe_session_profile_backfill',
+    sql: `
+      INSERT INTO vibe_session_profiles (session_id, user_id)
+      SELECT id, user_id FROM vibe_sessions
+      ON CONFLICT (session_id) DO NOTHING;
+    `,
+  },
 ];