feat(explore): let the album page be asked for the whole tracklist

An album the user holds part of showed only the tracks on disk, with
nothing to say the rest existed. The page could already draw the full
release with the missing rows dimmed -- it just could not be asked: the
automatic rule fires on `completeness.known`, which depends on the files
declaring a per-disc total, or failing that on the catalog's own
`total_tracks`.

Neither reaches most albums. #16 fixed the first input for anything
tagged from now on, and the second is worse than it looks: the published
artifact is from 2026-08-10 and the column landed on 08-16, so
`completenessAnswer()`'s catalog fallback answers 0 for every user until
the index job republishes. Measured, and noted on #88, which is the
publish that carries it.

So the control is explicit. A "Show the whole album" switch flips the
synthetic "Your Library" entry between the local files and the release,
which is the same rendering, reached deliberately rather than inferred.

Three things about it are load-bearing:

- `showFullTracklist` is a tri-state, `null` meaning "follow the
  automatic rule". The rule is right when it fires, and the switch has
  to agree with the page it is sitting on rather than starting out
  contradicting it -- a plain boolean would need its default recomputed
  every time the completeness answer moved underneath it. The user
  outranks the rule in both directions.
- `fullReleaseCluster()` falls back to the highest-scoring cluster.
  `findLibraryCluster` is a guess over the `inLibrary` flags and returns
  nothing at all when none are set, which is exactly the untagged
  library this exists for -- without the fallback the control would be
  absent precisely where it is needed. The sublabel names the release
  either way rather than leaving the user to wonder whose tracklist they
  are reading.
- It appears only where it can change what is on screen: against the
  library entry, with a release to switch to, and only when the two
  tracklists differ. A complete album's release has the same rows as its
  files, so the switch would redraw the same list and read as broken --
  the same test the version dropdown one section up already answers.

The accessible name is asserted rather than assumed, through the
browser's own computation. `wa-switch` happens to get it right, and for
a third reason again: its `<input role="switch">` sits inside a native
`<label>` that also holds the `<slot>`, so the name is computed across
the flattened tree from light-DOM text. This app has shipped the
opposite twice.

Closes #7

frontend/src/components/explore-album-details/explore-album-details.ts

@@ -193,6 +193,25 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
     @state() private selectedVersionKey: string = '';
     @state() private coverArtURL = '';
 
+    /**
+     * Whether to draw the whole release rather than only the files on
+     * disk — `null` while nobody has said, which is the automatic rule
+     * (`buildLibraryEntry`: show the release once the tags say the album
+     * is incomplete).
+     *
+     * It is a *tri-state* on purpose. The automatic rule is right when
+     * it fires and the switch has to be able to agree with it, or the
+     * control would start out contradicting the page it is sitting on;
+     * a plain boolean would need its default recomputed every time the
+     * completeness answer changed underneath it.
+     *
+     * The rule alone was not enough, which is the report: it depends on
+     * the files declaring a per-disc total, so a library whose tags
+     * never said sat permanently on "only my tracks" with no way to ask
+     * for the rest — and no way to tell that there was a rest.
+     */
+    @state() private showFullTracklist: boolean | null = null;
+
     /**
      * The local album's own tracks — the authoritative answer to "what
      * is actually on disk," independent of `this.releases`, which
@@ -559,6 +578,19 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
             }
 
             /* ── Tracklist ── */
+            .tracklist-scope {
+                display: flex;
+                align-items: center;
+                flex-wrap: wrap;
+                gap: 6px 12px;
+                margin-bottom: 8px;
+            }
+
+            .tracklist-scope-hint {
+                font-size: var(--yj-text-xs);
+                color: var(--yj-text-tertiary, #888);
+            }
+
             .tracklist {
                 display: flex;
                 flex-direction: column;
@@ -914,6 +946,7 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
         this.releases = [];
         this.versionEntries = [];
         this.selectedVersionKey = '';
+        this.showFullTracklist = null;
         this.localTracks = [];
         this.filePaths = new Map();
         this.askedFor = new Set();
@@ -1817,17 +1850,23 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
             // Guarded on `known` rather than on "fewer tracks than the
             // cluster", which would swap in a catalog tracklist for
             // every album whose tags simply never declared a total.
+            //
+            // And guarded on the *user's* answer first, because the
+            // automatic rule can only fire where the tags declared a
+            // total: an album that says nothing is not an album that is
+            // complete, and it used to be shown as one.
             const answer = this.completenessAnswer();
-            const incomplete = answer?.known && !answer.complete;
 
-            if (incomplete) {
-                const fullRelease = this.findLibraryCluster(clusters);
+            if (this.showFullTracklist ?? (answer?.known && !answer.complete)) {
+                const fullRelease = this.fullReleaseCluster(clusters);
 
                 if (fullRelease) {
                     return {
                         key: 'synthetic:library',
                         label: 'Your Library',
-                        sublabel: `${answer?.owned ?? 0} of ${answer?.expected ?? 0} tracks · ${this.clusterLabel(fullRelease)}`,
+                        sublabel: answer?.known
+                            ? `${answer.owned} of ${answer.expected} tracks · ${this.clusterLabel(fullRelease)}`
+                            : `${this.clusterLabel(fullRelease)} · full tracklist`,
                         group: 'aggregate',
                         syntheticKind: 'library',
                         tracks: fullRelease.representative.tracks ?? [],
@@ -1861,6 +1900,25 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
         };
     }
 
+    /**
+     * The release to draw when the whole album is wanted rather than
+     * the files on disk.
+     *
+     * `findLibraryCluster` is the right answer where it has one — the
+     * release the user's tracks overlap most — but it is a guess over
+     * the `inLibrary` flags and returns nothing at all when none of
+     * them are set, which is every untagged library. Falling back to
+     * the highest-scoring cluster is what makes the switch work there;
+     * that is the same release the page would call "Standard", and the
+     * sublabel names it either way rather than leaving the user to
+     * wonder whose tracklist they are reading.
+     */
+    private fullReleaseCluster(
+        clusters: ReleaseCluster[],
+    ): ReleaseCluster | undefined {
+        return this.findLibraryCluster(clusters) ?? clusters[0];
+    }
+
     /**
      * Fallback only: used when there's no local album to anchor on
      * (see `buildLibraryEntry`). Finds the cluster with the highest
@@ -2238,6 +2296,7 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
                     @catalog-retry=${this.retryCatalog}
                 ></catalog-scope-notice>
                 ${this.renderVersionSelector()}
+                ${this.renderTracklistScope()}
                 ${this.renderTracklist()}
             </div>
             <track-details></track-details>
@@ -3036,6 +3095,86 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
 
     /* ── Tracklist ── */
 
+    /**
+     * "Show the whole album" — the switch between the files on disk and
+     * the release they are part of.
+     *
+     * The page could already draw the full release with the missing
+     * rows dimmed, and did so automatically once the tags said the
+     * album was incomplete. What it could not do was be *asked*: where
+     * the files declare no per-disc total and the catalog has none
+     * either, the rule never fires, so a partly-owned album showed only
+     * the tracks the user had and nothing said the rest existed.
+     *
+     * Three things about when it appears, all of them the same rule —
+     * a control that cannot change what is on screen is worse than no
+     * control, which is what the version dropdown's own guard is for:
+     *
+     * - Only against the synthetic "Your Library" entry. Every other
+     *   entry *is* a catalog tracklist already.
+     * - Only when a catalog release exists to switch to.
+     * - Only when the two differ. A complete album's release has the
+     *   same rows as its files, so the switch would redraw the same
+     *   list and read as broken.
+     */
+    private renderTracklistScope() {
+        const current = this.currentVersion();
+
+        if (current?.syntheticKind !== 'library') return nothing;
+        if (this.localTracks.length === 0) return nothing;
+
+        const full = this.fullReleaseCluster(this.clustersOf(this.versionEntries));
+        const fullCount = full?.representative.tracks?.length ?? 0;
+
+        if (fullCount === 0 || fullCount <= this.localTracks.length) {
+            return nothing;
+        }
+
+        const showing = current.tracks.length > this.localTracks.length;
+
+        return html`
+            <div class="tracklist-scope">
+                <wa-switch
+                    size="small"
+                    ?checked=${showing}
+                    @change=${this.handleTracklistScopeChange}
+                >
+                    Show the whole album
+                </wa-switch>
+                <span class="tracklist-scope-hint">
+                    ${showing
+                        ? `${this.localTracks.length} of ${fullCount} tracks are in your library`
+                        : `${fullCount - this.localTracks.length} more tracks are on this release`}
+                </span>
+            </div>
+        `;
+    }
+
+    /**
+     * The clusters behind the current entries.
+     *
+     * `buildClusters` computes them and keeps only the entries, so this
+     * recovers them rather than storing the array twice — two copies of
+     * a list rebuilt on four different events is how they come to
+     * disagree.
+     */
+    private clustersOf(entries: VersionEntry[]): ReleaseCluster[] {
+        return entries
+            .filter((e) => e.group === 'cluster')
+            .map((e) => e.cluster)
+            .filter((c): c is ReleaseCluster => !!c);
+    }
+
+    private handleTracklistScopeChange = (e: Event) => {
+        this.showFullTracklist = (e.target as HTMLInputElement).checked;
+
+        // The entries are derived, so the switch rebuilds them rather
+        // than patching the one it changed. `buildClusters` re-defaults
+        // the selection, which lands back on "Your Library" — the only
+        // entry this control is ever shown against.
+        this.buildClusters();
+    };
+
     /**
      * The heading is there and is not drawn.
      *