fix: soften vibe artist exclusions

backend/src/routes/v2.routes.ts

@@ -13,8 +13,10 @@ interface ActivePlan {
   servedTrackIds?: string[];
   /** Explicit feedback targets (skip, dislike, completion, promotion). */
   excludedTrackIds?: string[];
-  /** Main artists served or explicitly rejected in this session. */
-  excludedArtistIds?: string[];
+  /** Main artists already heard in this Vibe; they get a mild rank penalty. */
+  servedArtistIds?: string[];
+  /** Artists explicitly skipped/disliked; they receive the stronger penalty. */
+  downrankedArtistIds?: string[];
 }
 
 const PLAN_TTL_SEC = 2 * 3600;
@@ -26,9 +28,9 @@ function planKey(userId: string): string {
   return `v2:plan:${userId}`;
 }
 
-function appendUniqueTrackId(ids: string[] | undefined, trackId: string): string[] {
+function appendUniqueId(ids: string[] | undefined, id: string): string[] {
   const next = ids ? [...ids] : [];
-  if (!next.includes(trackId)) next.push(trackId);
+  if (!next.includes(id)) next.push(id);
   return next.length > MAX_SESSION_EXCLUSIONS
     ? next.slice(next.length - MAX_SESSION_EXCLUSIONS)
     : next;
@@ -41,8 +43,11 @@ function sessionExclusions(active: ActivePlan): string[] {
   ])];
 }
 
-function sessionArtistExclusions(active: ActivePlan): string[] {
-  return [...new Set(active.excludedArtistIds ?? [])];
+function sessionArtistPenalties(active: ActivePlan): Map<string, number> {
+  const penalties = new Map<string, number>();
+  for (const artistId of active.servedArtistIds ?? []) penalties.set(artistId, 0.2);
+  for (const artistId of active.downrankedArtistIds ?? []) penalties.set(artistId, 0.75);
+  return penalties;
 }
 
 export default async function v2Routes(fastify: FastifyInstance, options: { dbService: DbService; sessionDirector: SessionDirector }) {
@@ -148,7 +153,7 @@ export default async function v2Routes(fastify: FastifyInstance, options: { dbSe
       }
 
       const next = active.plan.shift()!;
-      active.servedTrackIds = appendUniqueTrackId(active.servedTrackIds, next.trackId);
+      active.servedTrackIds = appendUniqueId(active.servedTrackIds, next.trackId);
       const artistResult = await dbService.pgClient.query<{ artist_id: string }>(
         `SELECT artist_id FROM track_artists_v2
          WHERE track_id = $1 AND role = 'main'
@@ -156,7 +161,7 @@ export default async function v2Routes(fastify: FastifyInstance, options: { dbSe
         [next.trackId]
       );
       if (artistResult.rows[0]?.artist_id) {
-        active.excludedArtistIds = appendUniqueTrackId(active.excludedArtistIds, artistResult.rows[0].artist_id);
+        active.servedArtistIds = appendUniqueId(active.servedArtistIds, artistResult.rows[0].artist_id);
       }
       // Enrich with track details
       const track = await dbService.getTrackById(next.trackId);
@@ -169,7 +174,7 @@ export default async function v2Routes(fastify: FastifyInstance, options: { dbSe
           active.plan,
           [next.trackId],
           active.seedTrackId ?? undefined,
-          { excludedTrackIds: sessionExclusions(active), excludedArtistIds: sessionArtistExclusions(active) }
+          { excludedTrackIds: sessionExclusions(active), artistPenalties: sessionArtistPenalties(active) }
         );
         active.plan = refill;
       }
@@ -233,7 +238,8 @@ export default async function v2Routes(fastify: FastifyInstance, options: { dbSe
       if (!sessionId || active.sessionId !== sessionId) return 0;
       // Feedback may race /next or arrive after a client-side prefetch. In all
       // cases its track becomes ineligible for the rest of this session.
-      active.excludedTrackIds = appendUniqueTrackId(active.excludedTrackIds, trackId);
+      active.excludedTrackIds = appendUniqueId(active.excludedTrackIds, trackId);
+      if (action === 'skipped' || action === 'disliked') {
         const artistResult = await dbService.pgClient.query<{ artist_id: string }>(
           `SELECT artist_id FROM track_artists_v2
            WHERE track_id = $1 AND role = 'main'
@@ -241,7 +247,8 @@ export default async function v2Routes(fastify: FastifyInstance, options: { dbSe
           [trackId]
         );
         if (artistResult.rows[0]?.artist_id) {
-        active.excludedArtistIds = appendUniqueTrackId(active.excludedArtistIds, artistResult.rows[0].artist_id);
+          active.downrankedArtistIds = appendUniqueId(active.downrankedArtistIds, artistResult.rows[0].artist_id);
+        }
       }
       const sessionTrackIds = sessionExclusions(active);
       const refill = await director.replan(
@@ -250,7 +257,7 @@ export default async function v2Routes(fastify: FastifyInstance, options: { dbSe
         active.plan,
         [trackId],
         active.seedTrackId ?? undefined,
-        { excludedTrackIds: sessionTrackIds, excludedArtistIds: sessionArtistExclusions(active) }
+        { excludedTrackIds: sessionTrackIds, artistPenalties: sessionArtistPenalties(active) }
       );
       active.plan = refill;
       await setActivePlan(userId, active);

backend/src/services/session-director.service.ts

@@ -37,8 +37,12 @@ export interface RepetitionState {
 export interface PlanBuildOptions {
   /** Tracks already exposed during this Vibe session; they are ineligible. */
   excludedTrackIds?: Iterable<string>;
-  /** Main artists already served or rejected in this Vibe session. */
-  excludedArtistIds?: Iterable<string>;
+  /**
+   * Session-local artist penalties. These deliberately affect ranking rather
+   * than eligibility: a Vibe may return to an artist after giving other
+   * artists a fair chance, but skips/dislikes push that artist much lower.
+   */
+  artistPenalties?: Iterable<readonly [string, number]>;
 }
 
 const W_ENJOY = 1.0;
@@ -46,6 +50,7 @@ const W_FATIGUE = 0.4;
 const W_DIVERSITY = 0.3;
 const W_ENTROPY = 0.2;
 const W_REPETITION = 0.5;
+const W_SESSION_ARTIST_PENALTY = 0.5;
 const PLAN_SIZE = 20;
 
 /**
@@ -727,7 +732,8 @@ export class SessionDirector {
     fatigue: FatigueState,
     budgets: DiversityBudget[],
     state: GeneratorContext['state'],
-    repetitionState: RepetitionState
+    repetitionState: RepetitionState,
+    artistPenalties: ReadonlyMap<string, number> = new Map()
   ): Promise<Candidate[]> {
     if (candidates.length === 0) return [];
 
@@ -783,6 +789,11 @@ export class SessionDirector {
         + W_DIVERSITY * diversityBonus
         + W_ENTROPY * entropyBonus;
 
+      // Session history should diversify the queue, not make an artist
+      // permanently ineligible. A skipped/disliked artist receives the larger
+      // penalty supplied by the route; a merely served artist gets a small one.
+      score -= W_SESSION_ARTIST_PENALTY * (artistPenalties.get(artistId) ?? 0);
+
       if (wouldRepeat) {
         score *= 0.1;
       }
@@ -901,7 +912,7 @@ export class SessionDirector {
     ]);
     if (seedTrackId) recentExclusionSet.add(seedTrackId);
     const recentExclusions = [...recentExclusionSet];
-    const excludedArtistIds = new Set(options.excludedArtistIds ?? []);
+    const artistPenalties = new Map(options.artistPenalties ?? []);
     const toleranceMap: Record<string, number> = {};
     const discoveryBeliefs = allBeliefs.filter(b => b.profile === 'discovery');
     for (const b of discoveryBeliefs) {
@@ -938,15 +949,14 @@ export class SessionDirector {
     const eligibleCandidates = allCandidates.filter(candidate =>
       !recentExclusionSet.has(candidate.trackId) &&
       !repetitionState.recentTrackIds.has(candidate.trackId) &&
-      !repetitionState.recentArtistIds.has(candidateArtistMap.get(candidate.trackId) ?? '') &&
-      !excludedArtistIds.has(candidateArtistMap.get(candidate.trackId) ?? '')
+      !repetitionState.recentArtistIds.has(candidateArtistMap.get(candidate.trackId) ?? '')
     );
 
     if (eligibleCandidates.length === 0) {
       return [];
     }
     const ranked = await this.rankCandidates(
-      eligibleCandidates, fatigue, budgets, state, repetitionState
+      eligibleCandidates, fatigue, budgets, state, repetitionState, artistPenalties
     );
 
     const loopDim = await this.detectAntiLoop(state, fatigue, budgets, recentPlays);
@@ -1072,7 +1082,7 @@ export class SessionDirector {
       if (loopDim) {
         const rebuilt = await this.buildPlan(userId, sessionId, seedTrackId, {
           excludedTrackIds: new Set([...excludedTrackIds, ...remainingSlots.map(c => c.trackId)]),
-          excludedArtistIds: options.excludedArtistIds,
+          artistPenalties: options.artistPenalties,
         });
         return mergeUniquePlan(remainingSlots, rebuilt, excludedTrackIds, PLAN_SIZE);
       }
@@ -1082,7 +1092,7 @@ export class SessionDirector {
       if (Math.abs(entropy - 0.55) > 0.2) {
         const rebuilt = await this.buildPlan(userId, sessionId, seedTrackId, {
           excludedTrackIds: new Set([...excludedTrackIds, ...remainingSlots.map(c => c.trackId)]),
-          excludedArtistIds: options.excludedArtistIds,
+          artistPenalties: options.artistPenalties,
         });
         return mergeUniquePlan(remainingSlots, rebuilt, excludedTrackIds, PLAN_SIZE);
       }
@@ -1096,7 +1106,7 @@ export class SessionDirector {
     // queued. Keep the valid tail and append only fresh candidates.
     const rebuilt = await this.buildPlan(userId, sessionId, seedTrackId, {
       excludedTrackIds: new Set([...excludedTrackIds, ...remainingSlots.map(c => c.trackId)]),
-      excludedArtistIds: options.excludedArtistIds,
+      artistPenalties: options.artistPenalties,
     });
     return mergeUniquePlan(remainingSlots, rebuilt, excludedTrackIds, PLAN_SIZE);
   }

backend/src/services/session-director.test.ts

@@ -167,6 +167,28 @@ describe('SessionDirector', () => {
       const ranked = await director.rankCandidates(candidates, fatigue, budgets, state, repetitionState);
       expect(ranked[0].relevance).toBeGreaterThanOrEqual(ranked[ranked.length - 1].relevance);
     });
+
+    it('downranks a skipped artist without making it ineligible', async () => {
+      const db = makeMockDb();
+      (db.pgClient.query as any)
+        .mockResolvedValueOnce({ rows: [{ track_id: 't1', artist_id: 'a1' }, { track_id: 't2', artist_id: 'a2' }] })
+        .mockResolvedValueOnce({ rows: [] });
+      const director = new SessionDirector(db);
+      const candidates = [candidate('t1'), candidate('t2')];
+      const fatigue = { artist: new Map(), genre: new Map(), track: new Map(), language: new Map(), vocal: 0 };
+      const state = { energy: 0.5, noveltyHunger: 0.3, sessionAgeMin: 10, lastArtistIds: [], lastGenreIds: [], context: null };
+
+      const ranked = await director.rankCandidates(
+        candidates,
+        fatigue,
+        [],
+        state,
+        { recentTrackIds: new Set<string>(), recentArtistIds: new Set<string>() },
+        new Map([['a1', 0.75]])
+      );
+
+      expect(ranked.map(item => item.trackId)).toEqual(['t2', 't1']);
+    });
   });
 
   describe('buildState', () => {