backend/database/sql/queries/audio_files.sql

@@ -117,6 +117,9 @@ WHERE library_id = COALESCE(NULLIF(CAST(sqlc.arg(library_id) AS INTEGER), 0), li
 -- name: GetTrackByPath :one
 SELECT * FROM track_metadata WHERE file_path = ? LIMIT 1;
 
+-- name: GetTracksByPaths :many
+SELECT * FROM track_metadata WHERE file_path IN (sqlc.slice('paths'));
+
 -- name: GetTracksByAlbum :many
 SELECT * FROM track_metadata
 WHERE album_id = sqlc.arg(album_id)

backend/database/sql/sqlcgen/audio_files.sql.go

@@ -830,6 +830,71 @@ func (q *Queries) GetTracksByGenre(ctx context.Context, arg GetTracksByGenrePara
 	return items, nil
 }
 
+const getTracksByPaths = `-- name: GetTracksByPaths :many
+SELECT id, file_path, length_milliseconds, title, artist_name, track_number, disc_number, album, genre, year, release_year, composer, file_type, sample_rate, bit_depth, channels, bitrate, file_size, library_id, play_count, last_played, cover_art_path, artist_mbid, release_group_mbid, recording_mbid, album_id, artist_id FROM track_metadata WHERE file_path IN (/*SLICE:paths*/?)
+`
+
+func (q *Queries) GetTracksByPaths(ctx context.Context, paths []string) ([]TrackMetadatum, error) {
+	query := getTracksByPaths
+	var queryParams []interface{}
+	if len(paths) > 0 {
+		for _, v := range paths {
+			queryParams = append(queryParams, v)
+		}
+		query = strings.Replace(query, "/*SLICE:paths*/?", strings.Repeat(",?", len(paths))[1:], 1)
+	} else {
+		query = strings.Replace(query, "/*SLICE:paths*/?", "NULL", 1)
+	}
+	rows, err := q.db.QueryContext(ctx, query, queryParams...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []TrackMetadatum
+	for rows.Next() {
+		var i TrackMetadatum
+		if err := rows.Scan(
+			&i.ID,
+			&i.FilePath,
+			&i.LengthMilliseconds,
+			&i.Title,
+			&i.ArtistName,
+			&i.TrackNumber,
+			&i.DiscNumber,
+			&i.Album,
+			&i.Genre,
+			&i.Year,
+			&i.ReleaseYear,
+			&i.Composer,
+			&i.FileType,
+			&i.SampleRate,
+			&i.BitDepth,
+			&i.Channels,
+			&i.Bitrate,
+			&i.FileSize,
+			&i.LibraryID,
+			&i.PlayCount,
+			&i.LastPlayed,
+			&i.CoverArtPath,
+			&i.ArtistMbid,
+			&i.ReleaseGroupMbid,
+			&i.RecordingMbid,
+			&i.AlbumID,
+			&i.ArtistID,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Close(); err != nil {
+		return nil, err
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const lookupTrackMetaByPaths = `-- name: LookupTrackMetaByPaths :many
 SELECT id, file_path, title, artist_name, album, cover_art_path,
        artist_mbid, release_group_mbid, recording_mbid

backend/library/query.go

@@ -193,6 +193,48 @@ func (l *Library) GetTracks(libraryID int64) ([]Track, error) {
 	return tracksFromRows(rows), nil
 }
 
+// pathLookupChunk bounds the paths bound into one IN (...) query, well
+// under SQLite's bind-variable limit.
+const pathLookupChunk = 500
+
+// GetTracksByPaths returns whole tracks for the given file paths, in
+// the order asked, dropping any path that is not in the library.
+//
+// It is how the frontend resolves the tracks a surface is actually
+// showing (#279).  Track details from the queue, a playlist or a smart
+// playlist used to look the path up in the whole library's track
+// array, which had to be loaded first — so it was fetched eagerly at
+// startup, 20.5 MB at 26k tracks, to answer questions about a handful
+// of rows.
+func (l *Library) GetTracksByPaths(paths []string) ([]Track, error) {
+	byPath := make(map[string]Track, len(paths))
+
+	for start := 0; start < len(paths); start += pathLookupChunk {
+		chunk := paths[start:min(start+pathLookupChunk, len(paths))]
+
+		rows, err := l.db.ReadQueries.GetTracksByPaths(l.ctx, chunk)
+		if err != nil {
+			return nil, fmt.Errorf("could not get tracks by path: %w", err)
+		}
+
+		for _, row := range rows {
+			byPath[row.FilePath] = trackFromRow(row)
+		}
+	}
+
+	tracks := make([]Track, 0, len(byPath))
+
+	for _, path := range paths {
+		if t, ok := byPath[path]; ok {
+			tracks = append(tracks, t)
+			// A path asked twice is answered once.
+			delete(byPath, path)
+		}
+	}
+
+	return tracks, nil
+}
+
 // SearchTracks runs the library's FTS index and returns whole tracks.
 func (l *Library) SearchTracks(query string, libraryID int64) ([]Track, error) {
 	rows, err := l.db.SearchFTSTracks(query, libraryID, searchTrackLimit)

backend/library/trackpaths_test.go

@@ -0,0 +1,64 @@
+package library
+
+import (
+	"fmt"
+	"testing"
+)
+
+// #279: the track-details openers resolve the rows a surface is showing
+// by path, instead of finding them in the whole library's array.  The
+// answer must keep the caller's order (a batch dialog lists them as
+// selected), drop what is not in the library rather than invent it, and
+// survive more paths than one IN (...) can bind.
+func TestGetTracksByPaths(t *testing.T) {
+	t.Parallel()
+
+	lib, _ := setupTestLibrary(t)
+	seedAlbumsAndGenres(t, lib)
+
+	got, err := lib.GetTracksByPaths([]string{
+		"/other/b1.mp3", "/music/missing.mp3", "/music/a1.mp3", "/other/b1.mp3",
+	})
+	if err != nil {
+		t.Fatalf("GetTracksByPaths: %v", err)
+	}
+
+	paths := make([]string, 0, len(got))
+	for _, tr := range got {
+		paths = append(paths, tr.FilePath)
+	}
+
+	if want := "[/other/b1.mp3 /music/a1.mp3]"; fmt.Sprint(paths) != want {
+		t.Fatalf("paths = %v, want %s (caller order, missing dropped, duplicate once)", paths, want)
+	}
+
+	// Whole tracks, not just the key: details render every field.
+	if got[1].TrackName != "A1" || len(got[1].Genre) != 2 {
+		t.Errorf("a1 = %+v, want title A1 with two genres", got[1])
+	}
+}
+
+func TestGetTracksByPathsSpansChunks(t *testing.T) {
+	t.Parallel()
+
+	lib, _ := setupTestLibrary(t)
+	seedAlbumsAndGenres(t, lib)
+
+	// The real path last, behind more misses than one chunk binds, so a
+	// loop that only ran the first chunk would return nothing.
+	paths := make([]string, 0, pathLookupChunk+2)
+	for i := range pathLookupChunk + 1 {
+		paths = append(paths, fmt.Sprintf("/nowhere/%d.mp3", i))
+	}
+
+	paths = append(paths, "/music/a2.mp3")
+
+	got, err := lib.GetTracksByPaths(paths)
+	if err != nil {
+		t.Fatalf("GetTracksByPaths: %v", err)
+	}
+
+	if len(got) != 1 || got[0].FilePath != "/music/a2.mp3" {
+		t.Fatalf("got %d tracks (%v), want only /music/a2.mp3", len(got), got)
+	}
+}

frontend/bindings/yellowjacket/backend/library/library.ts

@@ -222,6 +222,21 @@ export function GetTracksByGenre(genre: string, libraryID: number): $Cancellable
     return $Call.ByID(1674220245, genre, libraryID);
 }
 
+/**
+ * GetTracksByPaths returns whole tracks for the given file paths, in
+ * the order asked, dropping any path that is not in the library.
+ * 
+ * It is how the frontend resolves the tracks a surface is actually
+ * showing (#279).  Track details from the queue, a playlist or a smart
+ * playlist used to look the path up in the whole library's track
+ * array, which had to be loaded first — so it was fetched eagerly at
+ * startup, 20.5 MB at 26k tracks, to answer questions about a handful
+ * of rows.
+ */
+export function GetTracksByPaths(paths: string[] | null): $CancellablePromise<$models.Track[] | null> {
+    return $Call.ByID(3966945290, paths);
+}
+
 /**
  * IsScanActive returns whether a scan is currently running.
  */

frontend/src/components/playlist-details/playlist-details.ts

@@ -56,12 +56,9 @@ import {
     createTrackCardDragImage,
     removeDragImage,
 } from '@utils/drag-image';
-import { libraryStore } from '@store/library-store';
 import '@components/playlist-picker/playlist-picker.js';
-import { loadTrackDetails } from '@utils/lazy-track-details.js';
-import { tracksByFilePath, tracksForPaths } from '@utils/track-index.js';
+import { showTrackDetailsForPath, showBatchTrackDetailsForPaths } from '@utils/track-details-opener.js';
 import type { TrackDetails } from '@components/track-details/track-details.js';
-import type { CoverArtUrls } from '@components/track-details/track-details.js';
 import '@components/phantom-resolver/phantom-resolver.js';
 import type { PhantomResolver } from '@components/phantom-resolver/phantom-resolver.js';
 import '@components/duplicate-tracks-dialog/duplicate-tracks-dialog.js';
@@ -758,76 +755,21 @@ export class PlaylistDetails
     }
 
     private async openTrackDetails(filePath: string) {
-        const tracks = libraryStore.getCachedTracks();
-        const track = tracks
-            ? tracksByFilePath(tracks).get(filePath)
-            : undefined;
-
-        if (!track) return;
-
-        const ready = await loadTrackDetails(
+        await showTrackDetailsForPath(
+            () => this.trackDetailsDialog,
+            filePath,
             () => void this.openTrackDetails(filePath),
         );
-
-        if (!ready) return;
-
-        const coverArt = track.CoverArtPath
-            ? {
-                coverArtPath: track.CoverArtPath,
-                coverArtSmall: track.CoverArtSmall,
-                coverArtMedium: track.CoverArtMedium,
-                coverArtLarge: track.CoverArtLarge,
-            }
-            : undefined;
-
-        this.trackDetailsDialog?.show(
-            track,
-            coverArt,
-        );
     }
 
     private async openBatchTrackDetails(
         filePaths: string[],
     ) {
-        const cachedTracks =
-            libraryStore.getCachedTracks();
-
-        if (!cachedTracks) return;
-
-        const tracks = tracksForPaths(
-            cachedTracks,
+        await showBatchTrackDetailsForPaths(
+            () => this.trackDetailsDialog,
             filePaths,
-        );
-
-        if (tracks.length === 0) return;
-
-        const ready = await loadTrackDetails(
             () => void this.openBatchTrackDetails(filePaths),
         );
-
-        if (!ready) return;
-
-        const first = tracks[0]!;
-        const albumNames = new Set(tracks.map((t) => t.Album));
-        let coverArt: CoverArtUrls | null = null;
-        let coverArtMixed = false;
-
-        if (albumNames.size === 1 && first.CoverArtPath) {
-            coverArt = {
-                coverArtPath: first.CoverArtPath,
-                coverArtSmall: first.CoverArtSmall,
-                coverArtMedium: first.CoverArtMedium,
-                coverArtLarge: first.CoverArtLarge,
-            };
-        } else if (albumNames.size > 1) {
-            coverArtMixed = true;
-        }
-
-        this.trackDetailsDialog?.showBatch(
-            tracks,
-            coverArt,
-            coverArtMixed,
-        );
     }
 
     /**

frontend/src/components/queue-panel/queue-panel.ts

@@ -51,12 +51,8 @@ import {
     createTrackCardDragImage,
     removeDragImage,
 } from '@utils/drag-image';
-import { libraryStore } from '@store/library-store';
-import type * as library from '@go/library/models.js';
-import { loadTrackDetails } from '@utils/lazy-track-details.js';
-import { tracksByFilePath } from '@utils/track-index.js';
+import { showTrackDetailsForPath, showBatchTrackDetailsForPaths } from '@utils/track-details-opener.js';
 import type { TrackDetails } from '@components/track-details/track-details.js';
-import type { CoverArtUrls } from '@components/track-details/track-details.js';
 import {
     creditLink,
     trackLink,
@@ -1542,90 +1538,30 @@ export class QueuePanel
     }
 
     private async openTrackDetails(index: number) {
-        const queueTrack =
-            this.queue.tracks[index];
+        const queueTrack = this.queue.tracks[index];
 
         if (!queueTrack) return;
 
-        const tracks =
-            libraryStore.getCachedTracks();
-        const track = tracks
-            ? tracksByFilePath(tracks).get(
-                queueTrack.filePath,
-            )
-            : undefined;
-
-        if (!track) return;
-
-        const ready = await loadTrackDetails(
+        await showTrackDetailsForPath(
+            () => this.trackDetailsDialog,
+            queueTrack.filePath,
             () => void this.openTrackDetails(index),
         );
-
-        if (!ready) return;
-
-        const coverArt = track.CoverArtPath
-            ? {
-                coverArtPath: track.CoverArtPath,
-                coverArtSmall: track.CoverArtSmall,
-                coverArtMedium: track.CoverArtMedium,
-                coverArtLarge: track.CoverArtLarge,
-            }
-            : undefined;
-
-        this.trackDetailsDialog?.show(
-            track,
-            coverArt,
-        );
     }
 
     private async openBatchTrackDetails(
         indices: number[],
     ) {
         const queueTracks = this.queue.tracks;
-        const cachedTracks =
-            libraryStore.getCachedTracks();
+        const filePaths = indices
+            .map((i) => queueTracks[i]?.filePath)
+            .filter((fp): fp is string => fp != null);
 
-        if (!cachedTracks) return;
-
-        const byPath = tracksByFilePath(cachedTracks);
-        const tracks = indices
-            .map((i) => queueTracks[i])
-            .filter((qt) => qt != null)
-            .map((qt) => byPath.get(qt.filePath))
-            .filter(
-                (t): t is library.Track =>
-                    t != null,
-            );
-
-        if (tracks.length === 0) return;
-
-        const ready = await loadTrackDetails(
+        await showBatchTrackDetailsForPaths(
+            () => this.trackDetailsDialog,
+            filePaths,
             () => void this.openBatchTrackDetails(indices),
         );
-
-        if (!ready) return;
-
-        const first = tracks[0]!;
-        const albumNames = new Set(tracks.map((t) => t.Album));
-        let coverArt: CoverArtUrls | null = null;
-        let coverArtMixed = false;
-
-        if (albumNames.size === 1 && first.CoverArtPath) {
-            coverArt = {
-                coverArtPath: first.CoverArtPath,
-                coverArtSmall: first.CoverArtSmall,
-                coverArtMedium: first.CoverArtMedium,
-                coverArtLarge: first.CoverArtLarge,
-            };
-        } else if (albumNames.size > 1) {
-            coverArtMixed = true;
-        }
-
-        this.trackDetailsDialog?.showBatch(
-            tracks,
-            coverArt,
-            coverArtMixed,
-        );
     }
 
     private onContextPlaylistActionComplete = () => {

frontend/src/components/smart-playlist-details/smart-playlist-details.ts

@@ -52,11 +52,8 @@ import '@lit-labs/virtualizer';
 import type { LitVirtualizer } from '@lit-labs/virtualizer';
 import { flow } from '@lit-labs/virtualizer/layouts/flow.js';
 import '@components/playlist-picker/playlist-picker.js';
-import { loadTrackDetails } from '@utils/lazy-track-details.js';
-import { tracksByFilePath, tracksForPaths } from '@utils/track-index.js';
+import { showTrackDetailsForPath, showBatchTrackDetailsForPaths } from '@utils/track-details-opener.js';
 import type { TrackDetails } from '@components/track-details/track-details.js';
-import type { CoverArtUrls } from '@components/track-details/track-details.js';
-import { libraryStore } from '@store/library-store';
 import { formatMilliseconds } from '@utils/time';
 import {
     creditLink,
@@ -1145,76 +1142,21 @@ export class SmartPlaylistDetails
     }
 
     private async openTrackDetails(filePath: string) {
-        const tracks = libraryStore.getCachedTracks();
-        const track = tracks
-            ? tracksByFilePath(tracks).get(filePath)
-            : undefined;
-
-        if (!track) return;
-
-        const ready = await loadTrackDetails(
+        await showTrackDetailsForPath(
+            () => this.trackDetailsDialog,
+            filePath,
             () => void this.openTrackDetails(filePath),
         );
-
-        if (!ready) return;
-
-        const coverArt = track.CoverArtPath
-            ? {
-                coverArtPath: track.CoverArtPath,
-                coverArtSmall: track.CoverArtSmall,
-                coverArtMedium: track.CoverArtMedium,
-                coverArtLarge: track.CoverArtLarge,
-            }
-            : undefined;
-
-        this.trackDetailsDialog?.show(
-            track,
-            coverArt,
-        );
     }
 
     private async openBatchTrackDetails(
         filePaths: string[],
     ) {
-        const cachedTracks =
-            libraryStore.getCachedTracks();
-
-        if (!cachedTracks) return;
-
-        const tracks = tracksForPaths(
-            cachedTracks,
+        await showBatchTrackDetailsForPaths(
+            () => this.trackDetailsDialog,
             filePaths,
-        );
-
-        if (tracks.length === 0) return;
-
-        const ready = await loadTrackDetails(
             () => void this.openBatchTrackDetails(filePaths),
         );
-
-        if (!ready) return;
-
-        const first = tracks[0]!;
-        const albumNames = new Set(tracks.map((t) => t.Album));
-        let coverArt: CoverArtUrls | null = null;
-        let coverArtMixed = false;
-
-        if (albumNames.size === 1 && first.CoverArtPath) {
-            coverArt = {
-                coverArtPath: first.CoverArtPath,
-                coverArtSmall: first.CoverArtSmall,
-                coverArtMedium: first.CoverArtMedium,
-                coverArtLarge: first.CoverArtLarge,
-            };
-        } else if (albumNames.size > 1) {
-            coverArtMixed = true;
-        }
-
-        this.trackDetailsDialog?.showBatch(
-            tracks,
-            coverArt,
-            coverArtMixed,
-        );
     }
 
     // =================================================================

frontend/src/components/track-details/track-details.ts

@@ -22,7 +22,8 @@ import {
 import { GetTrackMBIDs } from '@go/library/library.js';
 type TrackMBIDs = library.TrackMBIDs;
 import { ImageFilePicker, ReadFile } from '@go/frontendutil/frontendutil.js';
-import { libraryStore } from '../../store/library-store';
+import { trackCache } from '../../store/track-cache';
+import { batchCoverArt } from '@utils/track-details-opener.js';
 import { EventsOn } from '@runtime/runtime';
 import { Events } from '../../events';
 
@@ -1317,10 +1318,13 @@ export class TrackDetails extends LitElement {
         const container = img.parentElement;
 
         if (container) {
-            container.innerHTML =
-                '<div class="cover-placeholder">' +
-                '<wa-icon name="music"></wa-icon>' +
-                '</div>';
+            const placeholder = document.createElement('div');
+            const icon = document.createElement('wa-icon');
+
+            placeholder.className = 'cover-placeholder';
+            icon.setAttribute('name', 'music');
+            placeholder.append(icon);
+            container.replaceChildren(placeholder);
         }
     };
 
@@ -1690,20 +1694,11 @@ export class TrackDetails extends LitElement {
             // invalidation, which refreshes all other views.
             this.exitEditMode();
 
-            // Re-fetch track and album data so the dialog
-            // shows updated values and cover art.  The store
-            // invalidation is already in-flight from the event;
-            // these calls await the pending fetch or start one.
-            // Awaited for the side effect of refreshing the
-            // store; the album list is consumed elsewhere.
-            const [tracks] = await Promise.all([
-                libraryStore.getTracks(),
-                libraryStore.getAlbums(),
-            ]);
-
-            const updated = tracks.find(
-                (t) => t.FilePath === filePath,
-            );
+            // Re-read this one track so the dialog shows the
+            // values and cover art just written. Not the whole
+            // library (#279): the views that hold it refetch on
+            // the event, and only if something is showing them.
+            const [updated] = await trackCache.refresh([filePath]);
 
             if (updated) {
                 this.track = updated;
@@ -1828,39 +1823,18 @@ export class TrackDetails extends LitElement {
         this.errorMessage = '';
         this.cleanupPendingCoverArt();
 
-        // Refresh data from library store; album list is
-        // refreshed for side effects only.
-        const [tracks] = await Promise.all([
-            libraryStore.getTracks(),
-            libraryStore.getAlbums(),
-        ]);
+        // Re-read the tracks just written, in the order the batch
+        // holds them (#279) — not the whole library to filter.
+        // `refresh`, because the write's event may not have reached
+        // the cache before its own result did.
+        const refreshed = await trackCache.refresh(this.batchFilePaths);
 
-        // Re-resolve batch tracks.
-        const pathSet = new Set(this.batchFilePaths);
-        const refreshed = tracks.filter((t) =>
-            pathSet.has(t.FilePath),
-        );
         this.batchTracks = refreshed;
 
-        // Re-resolve cover art state.
-        const first = refreshed[0];
-        const albumNames = new Set(refreshed.map((t) => t.Album));
+        const { coverArt, mixed } = batchCoverArt(refreshed);
 
-        if (albumNames.size === 1 && first?.CoverArtPath) {
-            this.coverArt = {
-                coverArtPath: first.CoverArtPath,
-                coverArtSmall: first.CoverArtSmall,
-                coverArtMedium: first.CoverArtMedium,
-                coverArtLarge: first.CoverArtLarge,
-            };
-            this.batchCoverArtMixed = false;
-        } else if (albumNames.size > 1) {
-            this.coverArt = null;
-            this.batchCoverArtMixed = true;
-        } else {
-            this.coverArt = null;
-            this.batchCoverArtMixed = false;
-        }
+        this.coverArt = coverArt;
+        this.batchCoverArtMixed = mixed;
     };
 
     // -- Shared edit logic --
@@ -2103,6 +2077,8 @@ export class TrackDetails extends LitElement {
             // as a base64-encoded string (standard encoding/json
             // behaviour for []byte).
             const result = await ReadFile(filePath);
+            // SAFETY: the binding is typed as the Go []byte, but the
+            // wire value is the base64 string encoding/json made of it.
             const b64 = result as unknown as string;
             const binary = atob(b64);
             const bytes = new Uint8Array(binary.length);

frontend/src/store/track-cache.ts

@@ -0,0 +1,240 @@
+/**
+ * Whole tracks, looked up by file path, for the rows a surface is
+ * actually showing (#279).
+ *
+ * Track details from the queue, a playlist or a smart playlist used to
+ * find their track in `libraryStore`'s whole-library array. That made
+ * the array a dependency of every surface that can open details, so it
+ * was fetched eagerly at startup — 20.5 MB of JSON at 26 138 tracks —
+ * and when it had *not* landed yet, the openers that read it
+ * synchronously did nothing at all. This asks the backend for the
+ * paths in hand instead.
+ *
+ * Three things are load-bearing, the same three as `credit-store`:
+ *
+ * **Lookups are coalesced.** Every `get()` made in the same task joins
+ * one `GetTracksByPaths` call. A timer rather than a frame: these are
+ * user actions, not row renders, and a frame never fires in a hidden
+ * window, which would leave the caller waiting on nothing.
+ *
+ * **It is bounded.** A batch details dialog over "Select all" asks for
+ * every track in the library; it gets every one of them back, but the
+ * cache keeps only the most recent `TRACK_CACHE_LIMIT`.
+ *
+ * **It forgets what changed.** The events that make `library-store`
+ * refetch drop the affected entries here, and a play count is patched
+ * in place, so a cached track is never older than the last event about
+ * it. An answer that was in flight across an invalidation is still
+ * returned to its caller (it was correct when asked) but not cached.
+ */
+
+import { EventsOn } from '@runtime/runtime';
+import { GetTracksByPaths } from '@go/library/library.js';
+import type * as library from '@go/library/models.js';
+import { list } from '@utils/binding';
+import { LRUMap } from '@utils/lru-map';
+import { registerCacheProbe } from '@utils/cache-stats';
+import { Events } from '../events';
+
+/**
+ * Tracks retained. A track is ~25 short fields, so this is a couple of
+ * megabytes at most — sized above any batch a person edits by hand,
+ * far below a library.
+ */
+export const TRACK_CACHE_LIMIT = 2_000;
+
+interface Waiter {
+    paths: readonly string[];
+    resolve: (tracks: library.Track[]) => void;
+    reject: (err: unknown) => void;
+}
+
+class TrackCache {
+    private cache = new LRUMap<string, library.Track>(TRACK_CACHE_LIMIT);
+
+    /** Requests collected in this task, answered by one binding call. */
+    private waiting: Waiter[] = [];
+
+    private flushHandle: ReturnType<typeof setTimeout> | null = null;
+
+    /** Bumped by every invalidation; an older answer is not cached. */
+    private gen = 0;
+
+    constructor() {
+        EventsOn(Events.LibraryScanComplete, () => this.clear());
+        EventsOn(Events.LibraryRemoved, () => this.clear());
+        EventsOn(Events.TrackMetadataChanged, (payload: unknown) => {
+            const p = payload as { filePath?: string } | null;
+
+            // A batch write names no paths: forget everything.
+            if (p?.filePath) this.forget([p.filePath]);
+            else this.clear();
+        });
+        EventsOn(Events.TracksRemovedFromLibrary, (payload: unknown) => {
+            const p = payload as { filePaths?: string[] } | null;
+
+            this.forget(p?.filePaths ?? []);
+        });
+        EventsOn(Events.TrackPlayCountChanged, (payload: unknown) => {
+            this.applyPlayCount(payload);
+        });
+
+        registerCacheProbe('tracks-by-path', () => ({
+            entries: this.cache.size,
+            chars: this.retainedChars(),
+            limit: TRACK_CACHE_LIMIT,
+        }));
+    }
+
+    /**
+     * The tracks at `paths`, in the order given, without the ones that
+     * are not in the library. Cached tracks are answered without a call.
+     */
+    get(paths: readonly string[]): Promise<library.Track[]> {
+        const answered = this.fromCache(paths);
+
+        if (answered) return Promise.resolve(answered);
+
+        return new Promise((resolve, reject) => {
+            this.waiting.push({ paths, resolve, reject });
+            this.flushHandle ??= setTimeout(() => void this.flush(), 0);
+        });
+    }
+
+    /** One track, or undefined when the path is not in the library. */
+    async getOne(path: string): Promise<library.Track | undefined> {
+        return (await this.get([path]))[0];
+    }
+
+    /**
+     * Ask the backend again for `paths`, ignoring the cache.
+     *
+     * For a caller that has just written to these files and must not be
+     * answered from before the write, whether or not the event that
+     * invalidates them has arrived yet.
+     */
+    refresh(paths: readonly string[]): Promise<library.Track[]> {
+        this.forget(paths);
+
+        return this.get(paths);
+    }
+
+    /** Every path cached, or null if any is missing. */
+    private fromCache(paths: readonly string[]): library.Track[] | null {
+        const tracks: library.Track[] = [];
+
+        for (const path of paths) {
+            const track = this.cache.get(path);
+
+            if (!track) return null;
+
+            tracks.push(track);
+        }
+
+        return tracks;
+    }
+
+    private async flush(): Promise<void> {
+        this.flushHandle = null;
+
+        const waiting = this.waiting;
+
+        this.waiting = [];
+
+        const missing = new Set<string>();
+
+        for (const w of waiting) {
+            for (const path of w.paths) {
+                if (!this.cache.has(path)) missing.add(path);
+            }
+        }
+
+        const gen = this.gen;
+        let fetched: library.Track[];
+
+        try {
+            fetched = missing.size > 0
+                ? await list(GetTracksByPaths([...missing]))
+                : [];
+        } catch (err) {
+            for (const w of waiting) w.reject(err);
+
+            return;
+        }
+
+        // Answer from what this call returned plus what was cached when
+        // it was made — not from the cache afterwards, which an LRU
+        // eviction or an invalidation may have emptied in between.
+        const answer = new Map<string, library.Track>();
+
+        for (const w of waiting) {
+            for (const path of w.paths) {
+                const hit = this.cache.get(path);
+
+                if (hit) answer.set(path, hit);
+            }
+        }
+
+        for (const track of fetched) {
+            answer.set(track.FilePath, track);
+
+            if (gen === this.gen) this.cache.set(track.FilePath, track);
+        }
+
+        for (const w of waiting) {
+            const tracks: library.Track[] = [];
+
+            for (const path of w.paths) {
+                const track = answer.get(path);
+
+                if (track) tracks.push(track);
+            }
+
+            w.resolve(tracks);
+        }
+    }
+
+    private forget(paths: readonly string[]): void {
+        for (const path of paths) this.cache.delete(path);
+
+        this.gen++;
+    }
+
+    private clear(): void {
+        this.cache.clear();
+        this.gen++;
+    }
+
+    private applyPlayCount(payload: unknown): void {
+        const p = payload as {
+            filePath?: string;
+            playCount?: number;
+            lastPlayed?: string;
+        } | null;
+
+        if (!p?.filePath) return;
+
+        const existing = this.cache.get(p.filePath);
+
+        if (!existing) return;
+
+        this.cache.set(p.filePath, {
+            ...existing,
+            PlayCount: p.playCount ?? existing.PlayCount,
+            LastPlayed: p.lastPlayed ?? existing.LastPlayed,
+        });
+    }
+
+    private retainedChars(): number {
+        let total = 0;
+
+        for (const t of this.cache.values()) {
+            total += t.FilePath.length + t.TrackName.length
+                + t.ArtistName.length + t.Album.length;
+        }
+
+        return total;
+    }
+}
+
+export const trackCache = new TrackCache();

frontend/src/utils/track-details-opener.ts

@@ -8,12 +8,13 @@
  * one key both sides share, and turning it back into a track is the
  * work this does.
  *
- * `libraryStore.getTracks()` is awaited rather than
- * `getCachedTracks()`-and-bail (which is what `queue-panel` does):
- * Explore is reachable without ever opening the library views, so a
- * cold cache is ordinary here rather than a symptom, and silently doing
- * nothing on a menu item the user just clicked is not an option. The
- * fetch is the store's own, shared with every other reader.
+ * The queue, playlists and smart playlists are in the same position:
+ * they render their own row type, not a `library.Track`. All of them
+ * used to find the track in `libraryStore`'s whole-library array, which
+ * meant that array had to be loaded for details to open — and the ones
+ * that read it synchronously silently did nothing when it was not
+ * (#279). They ask `trackCache` for the paths in hand instead: one
+ * small call, coalesced, answered from cache the second time.
  */
 
 import type * as library from '@go/library/models.js';
@@ -21,9 +22,8 @@ import type {
     CoverArtUrls,
     TrackDetails,
 } from '@components/track-details/track-details.js';
-import { libraryStore } from '@store/library-store.js';
+import { trackCache } from '@store/track-cache.js';
 import { loadTrackDetails } from '@utils/lazy-track-details.js';
-import { tracksByFilePath } from '@utils/track-index.js';
 
 /** The cover art the dialog shows, or nothing when the track has none. */
 function coverArtOf(track: library.Track): CoverArtUrls | undefined {
@@ -37,6 +37,22 @@ function coverArtOf(track: library.Track): CoverArtUrls | undefined {
         : undefined;
 }
 
+/**
+ * The cover a batch dialog shows: the album's, when every track is on
+ * one album; none and `mixed` when they span several.
+ */
+export function batchCoverArt(
+    tracks: readonly library.Track[],
+): { coverArt: CoverArtUrls | null; mixed: boolean } {
+    const albums = new Set(tracks.map((t) => t.Album));
+
+    if (albums.size > 1) return { coverArt: null, mixed: true };
+
+    const first = tracks[0];
+
+    return { coverArt: first ? coverArtOf(first) ?? null : null, mixed: false };
+}
+
 /**
  * What became of the attempt.
  *
@@ -62,8 +78,7 @@ export async function showTrackDetailsForPath(
     filePath: string,
     retry: () => void,
 ): Promise<TrackDetailsOutcome> {
-    const tracks = await libraryStore.getTracks();
-    const track = tracksByFilePath(tracks).get(filePath);
+    const track = await trackCache.getOne(filePath);
 
     if (!track) return 'not-in-library';
 
@@ -75,3 +90,28 @@ export async function showTrackDetailsForPath(
 
     return 'shown';
 }
+
+/**
+ * Show the batch details dialog for the library tracks at `filePaths`,
+ * in that order. Paths not in the library are left out; when none are,
+ * nothing is shown.
+ */
+export async function showBatchTrackDetailsForPaths(
+    dialog: () => TrackDetails | undefined,
+    filePaths: readonly string[],
+    retry: () => void,
+): Promise<TrackDetailsOutcome> {
+    const tracks = await trackCache.get(filePaths);
+
+    if (tracks.length === 0) return 'not-in-library';
+
+    const ready = await loadTrackDetails(retry);
+
+    if (!ready) return 'chunk-failed';
+
+    const { coverArt, mixed } = batchCoverArt(tracks);
+
+    dialog()?.showBatch(tracks, coverArt, mixed);
+
+    return 'shown';
+}

frontend/test/components/explore-track-details.test.ts

@@ -28,7 +28,7 @@ import type { TrackDetails } from '@components/track-details/track-details';
 const ALBUM_TRACKS = 'library.Library.GetAlbumTracks';
 const COMPLETENESS = 'library.Library.GetAlbumCompleteness';
 const FILE_PATHS = 'library.Library.GetFilePathsByRecordingMBIDs';
-const ALL_TRACKS = 'library.Library.GetTracks';
+const TRACKS_BY_PATH = 'library.Library.GetTracksByPaths';
 const LOOKUP_RG = 'explore.Service.LookupReleaseGroup';
 const BROWSE_RELEASES = 'explore.Service.BrowseReleases';
 
@@ -127,14 +127,13 @@ describe('Explore track details', () => {
     stub(ALBUM_TRACKS, [albumTrack]);
     stub(COMPLETENESS, { known: true, complete: true, owned: 1, expected: 1 });
     stub(FILE_PATHS, { [MBID]: [PATH] });
-    stub(ALL_TRACKS, [libraryTrack]);
+    stub(TRACKS_BY_PATH, [libraryTrack]);
   });
 
   /**
-   * `libraryStore` fetches at import and caches the empty list the
-   * shared setup stubs, for the life of the browser session — so a test
-   * that wants tracks in it has to say so. A scan-complete event is how
-   * the app itself invalidates that cache.
+   * `trackCache` keeps what it was answered for the life of the browser
+   * session, so a test that changes the answer has to drop it. A
+   * scan-complete event is how the app itself invalidates that cache.
    */
   async function primeLibrary() {
     emit(Events.LibraryScanComplete);
@@ -204,7 +203,7 @@ describe('Explore track details', () => {
     items[details]!.dispatchEvent(new MouseEvent('click', { bubbles: true }));
 
     // Polled rather than counted: the opener is three awaits deep — the
-    // path lookup, the store's tracks, and the dynamic `import()` of
+    // path lookup, the track by path, and the dynamic `import()` of
     // the dialog chunk — and a chunk fetch is the one of the three
     // whose cost depends on what else the suite is doing.
     const shown = await dialogTrack(el);
@@ -230,7 +229,7 @@ describe('Explore track details', () => {
   });
 
   it('reports a path with no library track rather than opening empty', async () => {
-    stub(ALL_TRACKS, []);
+    stub(TRACKS_BY_PATH, []);
     await primeLibrary();
 
     const outcome = await showTrackDetailsForPath(

frontend/test/components/lazy-track-details.test.ts

@@ -51,8 +51,12 @@ describe('track-details stays out of the startup chunk', () => {
         },
     );
 
+    // Directly, or through `utils/track-details-opener`, which awaits
+    // it and is what the path-keyed openers share (#279).
     it.each(OPENERS)('%s loads it at the point of use', (_name, source) => {
-        expect(source).toContain('loadTrackDetails');
+        expect(source).toMatch(
+            /loadTrackDetails|showTrackDetailsForPath|showBatchTrackDetailsForPaths/,
+        );
     });
 });
 

frontend/test/stores/track-cache.test.ts

@@ -0,0 +1,209 @@
+/**
+ * `trackCache` answers "which track is at this path" for the rows a
+ * surface is showing (#279), instead of every surface reaching into the
+ * whole library's array — which had to be fetched eagerly at startup
+ * for that to work, and silently did nothing when it had not been.
+ */
+import { describe, expect, it, beforeEach } from 'vitest';
+
+import { trackCache } from '@store/track-cache';
+import { libraryStore } from '@store/library-store';
+import { showBatchTrackDetailsForPaths } from '@utils/track-details-opener';
+import type { TrackDetails } from '@components/track-details/track-details';
+import { Events } from '../../src/events';
+import {
+  calls,
+  emit,
+  flush,
+  resetHarness,
+  stub,
+  stubFailure,
+} from '@test/support/harness';
+
+const BY_PATHS = 'library.Library.GetTracksByPaths';
+
+function track(path: string, album = 'Album') {
+  return {
+    FilePath: path,
+    TrackName: path,
+    ArtistName: 'Artist',
+    Album: album,
+    PlayCount: 0,
+    LastPlayed: '',
+    CoverArtPath: '',
+  };
+}
+
+/** The backend: answers every path that starts with /lib/. */
+function stubLibrary(): void {
+  stub(BY_PATHS, (paths: string[]) =>
+    paths.filter((p) => p.startsWith('/lib/')).map((p) => track(p)),
+  );
+}
+
+describe('track cache', () => {
+  beforeEach(() => {
+    // The cache is a singleton; a scan completing is how the app empties it.
+    emit(Events.LibraryScanComplete);
+    resetHarness();
+    stubLibrary();
+  });
+
+  it('answers in the order asked and leaves out paths not in the library', async () => {
+    const got = await trackCache.get(['/lib/b', '/gone', '/lib/a']);
+
+    expect(got.map((t) => t.FilePath)).toEqual(['/lib/b', '/lib/a']);
+  });
+
+  it('coalesces lookups made together into one call', async () => {
+    await Promise.all([
+      trackCache.get(['/lib/a']),
+      trackCache.get(['/lib/b', '/lib/a']),
+      trackCache.getOne('/lib/c'),
+    ]);
+
+    expect(calls(BY_PATHS)).toHaveLength(1);
+    expect((calls(BY_PATHS)[0]!.args[0] as string[]).sort()).toEqual([
+      '/lib/a',
+      '/lib/b',
+      '/lib/c',
+    ]);
+  });
+
+  it('answers a repeat from cache, and asks again after a retag of that file', async () => {
+    await trackCache.get(['/lib/a', '/lib/b']);
+    await trackCache.get(['/lib/a', '/lib/b']);
+    expect(calls(BY_PATHS)).toHaveLength(1);
+
+    emit(Events.TrackMetadataChanged, { filePath: '/lib/a' });
+    await trackCache.get(['/lib/b']);
+    expect(calls(BY_PATHS), 'an unchanged file is still cached').toHaveLength(1);
+
+    await trackCache.get(['/lib/a']);
+    expect(calls(BY_PATHS)).toHaveLength(2);
+  });
+
+  it('patches a play count in place without a call', async () => {
+    await trackCache.getOne('/lib/a');
+    emit(Events.TrackPlayCountChanged, {
+      filePath: '/lib/a',
+      playCount: 7,
+      lastPlayed: '2026-10-05 10:00:00',
+    });
+
+    const got = await trackCache.getOne('/lib/a');
+
+    expect([got?.PlayCount, got?.LastPlayed, calls(BY_PATHS).length]).toEqual([
+      7,
+      '2026-10-05 10:00:00',
+      1,
+    ]);
+  });
+
+  it('does not cache an answer that crossed an invalidation', async () => {
+    let answer: (v: unknown) => void = () => undefined;
+
+    stub(BY_PATHS, () => new Promise((resolve) => {
+      answer = resolve;
+    }));
+
+    const pending = trackCache.getOne('/lib/a');
+
+    // Sent, not yet answered: the invalidation lands in between.
+    await flush();
+    expect(calls(BY_PATHS)).toHaveLength(1);
+    emit(Events.TrackMetadataChanged, { batch: true });
+    answer([track('/lib/a')]);
+    expect((await pending)?.FilePath, 'the caller still gets it').toBe('/lib/a');
+
+    stubLibrary();
+
+    await trackCache.getOne('/lib/a');
+    expect(calls(BY_PATHS)).toHaveLength(2);
+  });
+
+  it('rejects every waiter in a batch when the call fails', async () => {
+    stubFailure(BY_PATHS);
+
+    const results = await Promise.allSettled([
+      trackCache.getOne('/lib/a'),
+      trackCache.getOne('/lib/b'),
+    ]);
+
+    expect(results.map((r) => r.status)).toEqual(['rejected', 'rejected']);
+  });
+});
+
+/*
+ * The bug half of #279: the queue, playlist and smart-playlist openers
+ * read `libraryStore.getCachedTracks()` and returned silently when it
+ * was null. The batch opener is what all three call now, so it is
+ * asserted against a library store that has nothing loaded.
+ */
+describe('opening details with no library list loaded', () => {
+  beforeEach(() => {
+    emit(Events.LibraryScanComplete);
+    resetHarness();
+    stubLibrary();
+    stub('library.Library.GetTracks', []);
+  });
+
+  it('shows the dialog with the tracks asked for', async () => {
+    await flush();
+    expect(libraryStore.getCachedTracks()?.length ?? 0).toBe(0);
+
+    let shown: unknown[] | null = null;
+    const dialog = {
+      showBatch: (tracks: unknown[]) => {
+        shown = tracks;
+      },
+    } as unknown as TrackDetails;
+
+    const outcome = await showBatchTrackDetailsForPaths(
+      () => dialog,
+      ['/lib/a', '/lib/b'],
+      () => undefined,
+    );
+
+    expect(outcome).toBe('shown');
+    expect((shown ?? []).map((t) => (t as { FilePath: string }).FilePath)).toEqual([
+      '/lib/a',
+      '/lib/b',
+    ]);
+  });
+});
+
+/** Every source file, as text. */
+const SOURCES = import.meta.glob<string>('../../src/**/*.ts', {
+  eager: true,
+  query: '?raw',
+  import: 'default',
+});
+
+/**
+ * Who may read the whole library's track array. The store owns it and
+ * the Tracks view draws it; anything else that needs a track by path
+ * asks `trackCache`, or the array becomes a startup dependency again.
+ */
+const MAY_READ_ALL_TRACKS = [
+  'store/library-store.ts',
+  'store/controllers/library-controller.ts',
+  'components/track-list/track-list.ts',
+];
+
+const ALL_TRACKS_READ = /getCachedTracks\(|libraryStore\.getTracks\(|\bcachedTracks\b/;
+
+describe('the whole-library track array has one reader', () => {
+  it('reads the sources it sweeps', () => {
+    expect(Object.keys(SOURCES).length).toBeGreaterThan(100);
+  });
+
+  it('is read only by the store and the Tracks view', () => {
+    const readers = Object.entries(SOURCES)
+      .filter(([, src]) => ALL_TRACKS_READ.test(src))
+      .map(([path]) => path.replace('../../src/', ''))
+      .sort();
+
+    expect(readers).toEqual([...MAY_READ_ALL_TRACKS].sort());
+  });
+});