feat(suggestions): adaptive artist selection and duplicate filtering

- Add extractAdaptiveArtists() for dynamic seed artist count based on playlist size
- Mix 60% top artists (coherence) + 40% random (discovery) for variety
- Filter duplicates by title+artist, not just track ID
- Catches same song from compilations, live albums, remasters, etc.
- Deduplicate within suggestion pool itself

src/lib/components/PlaylistSuggestions.svelte

@@ -16,6 +16,8 @@
     playlistId: number;
     artists: PlaylistArtist[];
     excludeTrackIds: number[];
+    /** Existing tracks in playlist for title+artist deduplication */
+    existingTracks?: Array<{ title: string; artist?: string }>;
     onAddTrack?: (trackId: number) => Promise<void>;
     onGoToAlbum?: (albumId: string) => void;
     onGoToArtist?: (artistId: number) => void;
@@ -27,6 +29,7 @@
     playlistId,
     artists,
     excludeTrackIds,
+    existingTracks = [],
     onAddTrack,
     onGoToAlbum,
     onGoToArtist,
@@ -34,6 +37,42 @@
     showReasons = false
   }: Props = $props();
 
+  /**
+   * Normalize a string for comparison (lowercase, trim, remove extra whitespace)
+   */
+  function normalizeForComparison(str: string): string {
+    return str.toLowerCase().trim().replace(/\s+/g, ' ');
+  }
+
+  /**
+   * Create a key for title+artist deduplication
+   */
+  function makeTrackKey(title: string, artist: string): string {
+    return `${normalizeForComparison(title)}|${normalizeForComparison(artist)}`;
+  }
+
+  /**
+   * Build set of existing track keys for fast lookup
+   */
+  const existingTrackKeys = $derived.by(() => {
+    const keys = new Set<string>();
+    for (const track of existingTracks) {
+      if (track.title && track.artist) {
+        keys.add(makeTrackKey(track.title, track.artist));
+      }
+    }
+    return keys;
+  });
+
+  /**
+   * Check if a suggested track is a duplicate of an existing track
+   */
+  function isDuplicateOfExisting(track: SuggestedTrack): boolean {
+    if (!track.title || !track.artist_name) return false;
+    const key = makeTrackKey(track.title, track.artist_name);
+    return existingTrackKeys.has(key);
+  }
+
   // TrackInfo modal state
   let trackInfoOpen = $state(false);
   let trackInfoId = $state<number | null>(null);
@@ -81,9 +120,24 @@
 
   // Derived state
   const dismissedIds = $derived(getDismissedTrackIds(playlistId));
-  const filteredPool = $derived(
-    pool.filter(t => !dismissedIds.has(t.track_id) && !excludeTrackIds.includes(t.track_id))
-  );
+  const filteredPool = $derived.by(() => {
+    // First filter by ID and dismissed
+    const byId = pool.filter(t =>
+      !dismissedIds.has(t.track_id) && !excludeTrackIds.includes(t.track_id)
+    );
+
+    // Then filter by title+artist to avoid duplicates from compilations, live albums, etc.
+    const filtered = byId.filter(t => !isDuplicateOfExisting(t));
+
+    // Also deduplicate within the pool itself (same song from different albums)
+    const seenKeys = new Set<string>();
+    return filtered.filter(t => {
+      const key = makeTrackKey(t.title, t.artist_name);
+      if (seenKeys.has(key)) return false;
+      seenKeys.add(key);
+      return true;
+    });
+  });
   const totalPages = $derived(Math.ceil(filteredPool.length / VISIBLE_COUNT));
   const visibleTracks = $derived(
     filteredPool.slice(currentPage * VISIBLE_COUNT, (currentPage + 1) * VISIBLE_COUNT)

src/lib/components/views/PlaylistDetailView.svelte

@@ -8,7 +8,7 @@
   import { open } from '@tauri-apps/plugin-dialog';
   import TrackRow from '../TrackRow.svelte';
   import PlaylistSuggestions from '../PlaylistSuggestions.svelte';
-  import { extractTopArtists } from '$lib/services/playlistSuggestionsService';
+  import { extractAdaptiveArtists } from '$lib/services/playlistSuggestionsService';
   import { type OfflineCacheStatus } from '$lib/stores/offlineCacheState';
   import {
     subscribe as subscribeOffline,
@@ -194,9 +194,10 @@
   let localTracksDuration = $derived(localTracks.reduce((sum, t) => sum + t.duration_secs, 0));
   let totalDuration = $derived((playlist?.duration ?? 0) + localTracksDuration);
 
-  // Playlist suggestions: extract top 5 artists by track count (not local tracks)
+  // Playlist suggestions: adaptive artist selection (quantity scales with playlist size,
+  // mix of top artists for coherence + random artists for discovery)
   const playlistArtists = $derived(
-    extractTopArtists(tracks.filter(t => !t.isLocal), 5)
+    extractAdaptiveArtists(tracks.filter(t => !t.isLocal))
   );
   // Track IDs to exclude from suggestions (already in playlist)
   const excludeTrackIds = $derived(
@@ -1702,6 +1703,7 @@
         playlistId={playlistId}
         artists={playlistArtists}
         excludeTrackIds={excludeTrackIds}
+        existingTracks={tracks.filter(t => !t.isLocal).map(t => ({ title: t.title, artist: t.artist }))}
         onAddTrack={handleAddSuggestedTrack}
         onGoToAlbum={onTrackGoToAlbum}
         onGoToArtist={onTrackGoToArtist}

src/lib/services/playlistSuggestionsService.ts

@@ -161,18 +161,111 @@ export async function cleanupVectorStore(maxAgeDays?: number): Promise<number> {
 
 // ============ Helpers ============
 
-/** Default number of top artists to use for suggestions */
-const DEFAULT_TOP_ARTISTS = 30;
+/**
+ * Calculate adaptive artist limit based on playlist size
+ * Larger playlists = more seed artists for better discovery
+ */
+function calculateAdaptiveLimit(trackCount: number): number {
+  if (trackCount < 15) return Math.max(3, Math.min(5, trackCount));
+  if (trackCount < 50) return Math.min(10, Math.ceil(trackCount * 0.3));
+  if (trackCount < 100) return Math.min(15, Math.ceil(trackCount * 0.2));
+  return Math.min(20, Math.ceil(trackCount * 0.15));
+}
+
+/**
+ * Shuffle array using Fisher-Yates algorithm
+ */
+function shuffleArray<T>(array: T[]): T[] {
+  const result = [...array];
+  for (let i = result.length - 1; i > 0; i--) {
+    const j = Math.floor(Math.random() * (i + 1));
+    [result[i], result[j]] = [result[j], result[i]];
+  }
+  return result;
+}
+
+/**
+ * Extract artists from playlist tracks with adaptive quantity and mixed selection
+ *
+ * This function balances coherence (top artists by frequency) with discovery
+ * (random selection from less frequent artists).
+ *
+ * @param tracks - Playlist tracks
+ * @param options - Configuration options
+ * @param options.topRatio - Ratio of top artists vs random (default: 0.6 = 60% top, 40% random)
+ * @param options.forceLimit - Override adaptive limit with fixed number
+ */
+export function extractAdaptiveArtists(
+  tracks: Array<{ artist?: string; artistId?: number }>,
+  options: { topRatio?: number; forceLimit?: number } = {}
+): PlaylistArtist[] {
+  const { topRatio = 0.6, forceLimit } = options;
+
+  // Count tracks per artist
+  const artistCounts = new Map<string, { count: number; qobuzId?: number }>();
+
+  for (const track of tracks) {
+    if (track.artist) {
+      const existing = artistCounts.get(track.artist);
+      if (existing) {
+        existing.count++;
+      } else {
+        artistCounts.set(track.artist, { count: 1, qobuzId: track.artistId });
+      }
+    }
+  }
+
+  const uniqueArtistCount = artistCounts.size;
+  if (uniqueArtistCount === 0) return [];
+
+  // Calculate how many artists to select
+  const limit = forceLimit ?? calculateAdaptiveLimit(tracks.length);
+  const actualLimit = Math.min(limit, uniqueArtistCount);
+
+  // If we have few artists, just return all of them shuffled
+  if (uniqueArtistCount <= actualLimit) {
+    const all = [...artistCounts.entries()].map(([name, data]) => ({
+      name,
+      qobuzId: data.qobuzId
+    }));
+    return shuffleArray(all);
+  }
+
+  // Sort by count descending
+  const sorted = [...artistCounts.entries()]
+    .sort((a, b) => b[1].count - a[1].count);
+
+  // Split into top artists and the rest
+  const topCount = Math.max(1, Math.floor(actualLimit * topRatio));
+  const randomCount = actualLimit - topCount;
+
+  // Take top artists (coherence)
+  const topArtists = sorted.slice(0, topCount);
+
+  // Randomly select from remaining artists (discovery)
+  const remaining = sorted.slice(topCount);
+  const randomArtists = shuffleArray(remaining).slice(0, randomCount);
+
+  // Combine and shuffle the final selection
+  const combined = [...topArtists, ...randomArtists];
+  const shuffled = shuffleArray(combined);
+
+  return shuffled.map(([name, data]) => ({
+    name,
+    qobuzId: data.qobuzId
+  }));
+}
 
 /**
  * Extract top artists from playlist tracks, sorted by frequency (track count)
+ * @deprecated Use extractAdaptiveArtists for better discovery
  *
  * @param tracks - Playlist tracks
- * @param limit - Maximum number of artists to return (default: 5)
+ * @param limit - Maximum number of artists to return
  */
 export function extractTopArtists(
   tracks: Array<{ artist?: string; artistId?: number }>,
-  limit: number = DEFAULT_TOP_ARTISTS
+  limit: number = 30
 ): PlaylistArtist[] {
   // Count tracks per artist
   const artistCounts = new Map<string, { count: number; qobuzId?: number }>();