music: pool single-album artists into shared rows

An artist with one album got a heading and one cover on a row that fits
five, and a library is mostly single-album artists. Consecutive singles
share one grid, in place, so the page stays in artist order.

Each pooled cover keeps its artist's name above it in the same type as
a section heading. Dropping it was the first version and it was wrong:
scrolling then alternates between artists written large and small.

Measured on the probe's fixture: 4208px to 1895px, and a walk of the
page reaches all 21 covers instead of 9.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 76 insertions, 18 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/music-app.js b/packages/meshbay-hub/src/meshbay_hub/static/music-app.js
index 8fc6cb3..baa3520 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/music-app.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/music-app.js
@@ -348,10 +348,29 @@ function MusicDetailModal({ album, transportRef, gekRef, musicbrainzEnabled, onC
 
 // -- Mode A: album grid -----------------------------------------------------
 
-// `units` is one page of `{ artist, album }`. An artist whose albums straddle
-// two pages gets its heading on both.
-function AlbumGrid({ units, transportRef, gekRef, musicbrainzEnabled, onPlayQueue, onMenu }) {
-  const [detail, setDetail] = useState(null); // the album object
+/**
+ * One page of `{ artist, album }` as the sections that get drawn.
+ *
+ * An artist with two or more albums gets a heading and a grid of their own. An
+ * artist with **one** does not: a heading plus a single cover is a whole row of
+ * whitespace, and a library is mostly single-album artists — a compilation
+ * bought once, one album of someone's, a soundtrack. Consecutive singles share
+ * one grid instead, so five of them fill a row that five headings would
+ * otherwise have spent five rows on.
+ *
+ * Pooled in place rather than swept into a bin at the end: the page is drawn in
+ * artist order and a reader scrolling it is relying on that. A pooled run sits
+ * exactly where its artists would have been.
+ *
+ * **Each pooled cover keeps its artist's name above it, in the same type as a
+ * multi-album artist's heading.** The first version of this dropped the heading
+ * on the grounds that the card already names its artist underneath — and that
+ * was wrong: scrolling then alternates between artists written large and
+ * artists written small, and the eye has to work out which kind of row it is
+ * looking at. The heading moves *into* the cell rather than going away, so a
+ * row of five costs one heading's height between them instead of five rows.
+ */
+function albumSections(units) {
   const artists = [];
   for (const u of units) {
     const prev = artists[artists.length - 1];
@@ -359,21 +378,60 @@ function AlbumGrid({ units, transportRef, gekRef, musicbrainzEnabled, onPlayQueu
     else artists.push({ artist: u.artist, albums: [u.album] });
   }
 
+  const sections = [];
+  for (const a of artists) {
+    if (a.albums.length >= 2) { sections.push({ kind: 'artist', ...a }); continue; }
+    const prev = sections[sections.length - 1];
+    if (prev && prev.kind === 'pool') prev.albums.push(a.albums[0]);
+    else sections.push({ kind: 'pool', albums: [a.albums[0]] });
+  }
+  return sections;
+}
+
+// `units` is one page of `{ artist, album }`. An artist whose albums straddle
+// two pages gets its heading on both — and, with one album on each page, is
+// pooled on both.
+function AlbumGrid({ units, transportRef, gekRef, musicbrainzEnabled, onPlayQueue, onMenu }) {
+  const [detail, setDetail] = useState(null); // the album object
+  const sections = useMemo(() => albumSections(units), [units]);
+
+  const tile = (album) => html`
+    <${LazyTile} key=${album.artist + '::' + album.album} cls="music-tile-slot">
+      <${AlbumCard} album=${album} transportRef=${transportRef} gekRef=${gekRef}
+        musicbrainzEnabled=${musicbrainzEnabled} onOpen=${() => setDetail(album)}
+        onMenu=${onMenu} />
+    </${LazyTile}>
+  `;
+
+  // Keyed on the first album rather than on the index: a pool's position shifts
+  // whenever a neighbouring artist gains or loses an album, and an index key
+  // would make preact reuse the wrong tiles across that change.
+  const sectionKey = (s) => (s.kind === 'artist'
+    ? `artist:${s.artist}`
+    : `pool:${s.albums[0].artist}::${s.albums[0].album}`);
+
   return html`
-    ${artists.map((a) => html`
-      <div class="music-artist-section" key=${a.artist}>
-        <h3 class="music-artist-heading">${a.artist}</h3>
-        <div class="music-grid">
-          ${a.albums.map((album) => html`
-            <${LazyTile} key=${album.artist + '::' + album.album} cls="music-tile-slot">
-              <${AlbumCard} album=${album} transportRef=${transportRef} gekRef=${gekRef}
-                musicbrainzEnabled=${musicbrainzEnabled} onOpen=${() => setDetail(album)}
-                onMenu=${onMenu} />
-            </${LazyTile}>
-          `)}
-        </div>
-      </div>
-    `)}
+    ${sections.map((s) => (s.kind === 'artist'
+      ? html`
+        <div class="music-artist-section" key=${sectionKey(s)}>
+          <h3 class="music-artist-heading">${s.artist}</h3>
+          <div class="music-grid">${s.albums.map(tile)}</div>
+        </div>`
+      : html`
+        <div class="music-artist-section music-artist-pool" key=${sectionKey(s)}>
+          <div class="music-grid">
+            ${s.albums.map((album) => html`
+              <div class="music-pool-cell" key=${album.artist + '::' + album.album}>
+                ${/* One line, clipped, with the full name on hover: a cell is
+                     ~170px wide and a heading that wraps to two lines would
+                     push its own cover below the others on the row. */''}
+                <h3 class="music-artist-heading music-pool-heading"
+                  title=${album.artist}>${album.artist}</h3>
+                ${tile(album)}
+              </div>
+            `)}
+          </div>
+        </div>`))}
     ${detail && html`
       <${MusicDetailModal} album=${detail} transportRef=${transportRef} gekRef=${gekRef}
         musicbrainzEnabled=${musicbrainzEnabled} onMenu=${onMenu}