fix: rely on vibe fatigue instead of artist counters

backend/src/routes/v2.routes.ts

@@ -13,10 +13,6 @@ interface ActivePlan {
   servedTrackIds?: string[];
   /** Explicit feedback targets (skip, dislike, completion, promotion). */
   excludedTrackIds?: 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;
@@ -43,13 +39,6 @@ function sessionExclusions(active: ActivePlan): string[] {
   ])];
 }
 
-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 }) {
   const { dbService, sessionDirector: director } = options;
 
@@ -154,15 +143,6 @@ export default async function v2Routes(fastify: FastifyInstance, options: { dbSe
 
       const next = active.plan.shift()!;
       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'
-         ORDER BY confidence DESC NULLS LAST LIMIT 1`,
-        [next.trackId]
-      );
-      if (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);
 
@@ -174,7 +154,7 @@ export default async function v2Routes(fastify: FastifyInstance, options: { dbSe
           active.plan,
           [next.trackId],
           active.seedTrackId ?? undefined,
-          { excludedTrackIds: sessionExclusions(active), artistPenalties: sessionArtistPenalties(active) }
+          { excludedTrackIds: sessionExclusions(active) }
         );
         active.plan = refill;
       }
@@ -239,17 +219,6 @@ export default async function v2Routes(fastify: FastifyInstance, options: { dbSe
       // 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 = 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'
-           ORDER BY confidence DESC NULLS LAST LIMIT 1`,
-          [trackId]
-        );
-        if (artistResult.rows[0]?.artist_id) {
-          active.downrankedArtistIds = appendUniqueId(active.downrankedArtistIds, artistResult.rows[0].artist_id);
-        }
-      }
       const sessionTrackIds = sessionExclusions(active);
       const refill = await director.replan(
         userId,
@@ -257,7 +226,7 @@ export default async function v2Routes(fastify: FastifyInstance, options: { dbSe
         active.plan,
         [trackId],
         active.seedTrackId ?? undefined,
-        { excludedTrackIds: sessionTrackIds, artistPenalties: sessionArtistPenalties(active) }
+        { excludedTrackIds: sessionTrackIds }
       );
       active.plan = refill;
       await setActivePlan(userId, active);

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

@@ -37,12 +37,6 @@ export interface RepetitionState {
 export interface PlanBuildOptions {
   /** Tracks already exposed during this Vibe session; they are ineligible. */
   excludedTrackIds?: 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;
@@ -50,7 +44,6 @@ 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;
 
 /**
@@ -732,8 +725,7 @@ export class SessionDirector {
     fatigue: FatigueState,
     budgets: DiversityBudget[],
     state: GeneratorContext['state'],
-    repetitionState: RepetitionState,
-    artistPenalties: ReadonlyMap<string, number> = new Map()
+    repetitionState: RepetitionState
   ): Promise<Candidate[]> {
     if (candidates.length === 0) return [];
 
@@ -789,11 +781,6 @@ 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;
       }
@@ -912,7 +899,6 @@ export class SessionDirector {
     ]);
     if (seedTrackId) recentExclusionSet.add(seedTrackId);
     const recentExclusions = [...recentExclusionSet];
-    const artistPenalties = new Map(options.artistPenalties ?? []);
     const toleranceMap: Record<string, number> = {};
     const discoveryBeliefs = allBeliefs.filter(b => b.profile === 'discovery');
     for (const b of discoveryBeliefs) {
@@ -956,7 +942,7 @@ export class SessionDirector {
       return [];
     }
     const ranked = await this.rankCandidates(
-      eligibleCandidates, fatigue, budgets, state, repetitionState, artistPenalties
+      eligibleCandidates, fatigue, budgets, state, repetitionState
     );
 
     const loopDim = await this.detectAntiLoop(state, fatigue, budgets, recentPlays);
@@ -1082,7 +1068,6 @@ export class SessionDirector {
       if (loopDim) {
         const rebuilt = await this.buildPlan(userId, sessionId, seedTrackId, {
           excludedTrackIds: new Set([...excludedTrackIds, ...remainingSlots.map(c => c.trackId)]),
-          artistPenalties: options.artistPenalties,
         });
         return mergeUniquePlan(remainingSlots, rebuilt, excludedTrackIds, PLAN_SIZE);
       }
@@ -1092,7 +1077,6 @@ 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)]),
-          artistPenalties: options.artistPenalties,
         });
         return mergeUniquePlan(remainingSlots, rebuilt, excludedTrackIds, PLAN_SIZE);
       }
@@ -1106,7 +1090,6 @@ 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)]),
-      artistPenalties: options.artistPenalties,
     });
     return mergeUniquePlan(remainingSlots, rebuilt, excludedTrackIds, PLAN_SIZE);
   }

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

@@ -168,27 +168,6 @@ describe('SessionDirector', () => {
       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', () => {