feat(web): coupled section scrolling, earlier infinite-scroll, fuller player cover

Three coordinated polish changes:

1. PlayerBar cover bumps from h-20 (80px) to h-24 (96px) and the bar's
   vertical padding tightens from py-4 to py-1.5. Bar height stays
   ~108px but the cover now fills ~89% of it (was ~74%) — reads as the
   substantial primary content the operator wanted, not a thumbnail.

2. InfiniteScrollSentinel default rootMargin moves from 300px to 800px
   so the next page fetches well before the user reaches the bottom of
   the rendered set. Empirically that's ~3-4 rows of cards on a typical
   library grid — loading feels seamless rather than catching up.

3. HorizontalScrollRow takes rows: T[][] instead of items: T[]. Multiple
   rows of items now render inside one shared overflow-x-auto container,
   so the rows scroll together as a single coupled section. Recently
   added (2 album rows) and Most played (3 track rows) on the home page
   now scroll as one unit. Rediscover keeps two separate scrollers
   because its rows are different card types (square albums vs circular
   artists) — coupling those would interleave shapes awkwardly. The
   item snippet's second arg is now the global flat index so consumers
   like CompactTrackCard (which needs sectionTracks + index for play
   actions) work without per-row re-indexing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/components/HorizontalScrollRow.svelte

@@ -3,14 +3,24 @@
   import type { Snippet } from 'svelte';
 
   let {
-    items,
+    rows,
     item,
     title,
     ariaLabel
   }: {
-    items: T[];
+    /** One or more visual rows of items rendered inside a single shared
+        horizontal scroller. Pass [items] for a single-row section. */
+    rows: T[][];
+    /** Render snippet for a single item. The second arg is the global
+        index across the flattened sequence (rows[0] then rows[1] etc.) —
+        useful when the snippet needs section-wide indexing, e.g. a
+        compact track card whose play action takes its position in the
+        whole section's track list. */
     item?: Snippet<[T, number]>;
+    /** Section heading shown to the left of the arrows. Omit for an
+        unlabeled scroller. */
     title?: string;
+    /** Accessible label for the section as a whole. */
     ariaLabel?: string;
   } = $props();
 
@@ -22,6 +32,16 @@
   const atStart = $derived(scrollLeft <= 1);
   const atEnd   = $derived(scrollLeft + clientWidth >= scrollWidth - 1);
 
+  // Per-row offsets so the snippet's second arg can be the global index.
+  // [0, len(rows[0]), len(rows[0])+len(rows[1]), ...]
+  const rowOffsets = $derived.by(() => {
+    const out: number[] = [0];
+    for (let i = 0; i < rows.length - 1; i++) {
+      out.push(out[i] + rows[i].length);
+    }
+    return out;
+  });
+
   function refreshMetrics() {
     if (!scroller) return;
     scrollLeft  = scroller.scrollLeft;
@@ -39,8 +59,8 @@
   $effect(() => { refreshMetrics(); });
 </script>
 
-<div class="row" aria-label={ariaLabel}>
-  <header class="row-header">
+<div class="section" aria-label={ariaLabel}>
+  <header class="section-header">
     {#if title}
       <h2 class="font-display text-2xl font-medium text-text-primary">{title}</h2>
     {:else}
@@ -72,26 +92,32 @@
     bind:this={scroller}
     onscroll={refreshMetrics}
     data-testid="scroll-container"
-    class="scroller flex gap-4 overflow-x-auto"
+    class="scroller overflow-x-auto"
   >
-    {#each items as it, i (i)}
-      {@render item?.(it, i)}
-    {/each}
+    <div class="track inline-flex flex-col gap-4">
+      {#each rows as row, rowIdx (rowIdx)}
+        <div class="rack flex gap-4">
+          {#each row as it, colIdx (colIdx)}
+            {@render item?.(it, rowOffsets[rowIdx] + colIdx)}
+          {/each}
+        </div>
+      {/each}
+    </div>
   </div>
 </div>
 
 <style>
-  /* Bleed the row past the parent's right padding (16px from Shell's p-4)
+  /* Bleed the section past the parent's right padding (16px from Shell's p-4)
      so the scroller's items extend to the viewport's right edge. */
-  .row {
+  .section {
     margin-right: -1rem;
   }
-  .row-header {
+  .section-header {
     display: flex;
     align-items: center;
     justify-content: space-between;
-    /* Re-add the right gutter so the header stays aligned with the rest
-       of the page content (the scroller below remains full-bleed). */
+    /* Re-add the right gutter so the header stays aligned with page
+       content; the scroller below remains full-bleed. */
     padding-right: 1rem;
     margin-bottom: 0.5rem;
   }
@@ -103,7 +129,10 @@
     scroll-snap-type: x mandatory;
     scrollbar-width: thin;
   }
-  .scroller > :global(*) {
+  /* Cards are two levels deep (.scroller > .track > .rack > card-wrapper),
+     so target them via the rack. flex-shrink: 0 keeps each card at its
+     intended width even though the rack tries to fit the scroller width. */
+  .rack > :global(*) {
     flex-shrink: 0;
     scroll-snap-align: start;
   }

web/src/lib/components/HorizontalScrollRow.test.ts

@@ -6,18 +6,18 @@ afterEach(() => vi.clearAllMocks());
 
 describe('HorizontalScrollRow', () => {
   test('renders left and right scroll buttons', () => {
-    render(HorizontalScrollRow, { props: { items: ['a', 'b', 'c'] } });
+    render(HorizontalScrollRow, { props: { rows: [['a', 'b', 'c']] } });
     expect(screen.getByRole('button', { name: /scroll left/i })).toBeInTheDocument();
     expect(screen.getByRole('button', { name: /scroll right/i })).toBeInTheDocument();
   });
 
   test('left button starts disabled (scrollLeft is 0)', () => {
-    render(HorizontalScrollRow, { props: { items: ['a'] } });
+    render(HorizontalScrollRow, { props: { rows: [['a']] } });
     expect(screen.getByRole('button', { name: /scroll left/i })).toBeDisabled();
   });
 
   test('clicking right button calls scrollBy on the container', async () => {
-    const { container } = render(HorizontalScrollRow, { props: { items: ['a', 'b'] } });
+    const { container } = render(HorizontalScrollRow, { props: { rows: [['a', 'b']] } });
     const scroller = container.querySelector('[data-testid="scroll-container"]') as HTMLElement;
     const spy = vi.fn();
     scroller.scrollBy = spy as unknown as HTMLElement['scrollBy'];
@@ -31,12 +31,12 @@ describe('HorizontalScrollRow', () => {
   });
 
   test('renders title as a heading when prop is provided', () => {
-    render(HorizontalScrollRow, { props: { items: ['a'], title: 'My section' } });
+    render(HorizontalScrollRow, { props: { rows: [['a']], title: 'My section' } });
     expect(screen.getByRole('heading', { name: 'My section' })).toBeInTheDocument();
   });
 
   test('omits heading when title prop is absent', () => {
-    render(HorizontalScrollRow, { props: { items: ['a'] } });
+    render(HorizontalScrollRow, { props: { rows: [['a']] } });
     expect(screen.queryByRole('heading')).not.toBeInTheDocument();
   });
 });

web/src/lib/components/InfiniteScrollSentinel.svelte

@@ -9,10 +9,14 @@
   let {
     onIntersect,
     enabled = true,
-    rootMargin = '300px'
+    rootMargin = '800px'
   }: {
     onIntersect: () => void;
     enabled?: boolean;
+    /** Distance below the viewport at which the sentinel triggers. Larger
+        values fire earlier so the next page is fetched well before the
+        user scrolls into empty space. Default 800px ≈ 3-4 rows of
+        cards on a typical library grid. */
     rootMargin?: string;
   } = $props();
 

web/src/lib/components/PlayerBar.svelte

@@ -46,7 +46,7 @@
 </script>
 
 {#if current}
-  <div class="flex min-h-[108px] items-center gap-4 border-t border-border bg-surface px-4 py-4">
+  <div class="flex min-h-[108px] items-center gap-4 border-t border-border bg-surface px-4 py-1.5">
     <!-- Left: cover + title + artist + like + menu -->
     <div class="flex w-72 min-w-0 items-center gap-3">
       <a
@@ -57,7 +57,7 @@
         <img
           src={`/api/albums/${current.album_id}/cover`}
           alt=""
-          class="h-20 w-20 rounded-md object-cover"
+          class="h-24 w-24 rounded-md object-cover"
           onerror={onCoverError}
         />
       </a>

web/src/routes/+page.svelte

@@ -28,7 +28,7 @@
   {:else if showSkeleton.value && !data}
     <p class="text-text-secondary">Loading…</p>
   {:else if data}
-    <!-- Recently added: 50 albums in 2 rows of 25 -->
+    <!-- Recently added: 50 albums in 2 rows of 25, scrolling together -->
     <section class="space-y-3">
       {#if data.recently_added_albums.length === 0}
         <header>
@@ -36,21 +36,21 @@
         </header>
         <p class="text-text-secondary">Nothing added yet. Scan a folder via the server's config.</p>
       {:else}
-        {#each chunk(data.recently_added_albums, 25) as row, i (i)}
-          <HorizontalScrollRow
-            items={row}
-            title={i === 0 ? 'Recently added' : undefined}
-            ariaLabel="Recently added row {i + 1}"
-          >
-            {#snippet item(album: import('$lib/api/types').AlbumRef)}
-              <div class="w-44"><AlbumCard {album} /></div>
-            {/snippet}
-          </HorizontalScrollRow>
-        {/each}
+        <HorizontalScrollRow
+          rows={chunk(data.recently_added_albums, 25)}
+          title="Recently added"
+          ariaLabel="Recently added"
+        >
+          {#snippet item(album: import('$lib/api/types').AlbumRef)}
+            <div class="w-44"><AlbumCard {album} /></div>
+          {/snippet}
+        </HorizontalScrollRow>
       {/if}
     </section>
 
-    <!-- Rediscover: albums + artists -->
+    <!-- Rediscover: albums + artists. Kept as two scrollers because the
+         card types differ (square vs circular); coupling them in one
+         scroller would interleave shapes awkwardly. -->
     <section class="space-y-3">
       {#if data.rediscover_albums.length === 0 && data.rediscover_artists.length === 0}
         <header>
@@ -60,7 +60,7 @@
       {:else}
         {#if data.rediscover_albums.length > 0}
           <HorizontalScrollRow
-            items={data.rediscover_albums}
+            rows={[data.rediscover_albums]}
             title="Rediscover"
             ariaLabel="Rediscover albums"
           >
@@ -71,7 +71,7 @@
         {/if}
         {#if data.rediscover_artists.length > 0}
           <HorizontalScrollRow
-            items={data.rediscover_artists}
+            rows={[data.rediscover_artists]}
             title={data.rediscover_albums.length === 0 ? 'Rediscover' : undefined}
             ariaLabel="Rediscover artists"
           >
@@ -83,7 +83,7 @@
       {/if}
     </section>
 
-    <!-- Most played: 75 tracks in 3 rows of 25 -->
+    <!-- Most played: 75 tracks in 3 rows of 25, scrolling together -->
     <section class="space-y-3">
       {#if data.most_played_tracks.length === 0}
         <header>
@@ -91,21 +91,19 @@
         </header>
         <p class="text-text-secondary">No plays to draw from. Listen to something.</p>
       {:else}
-        {#each chunk(data.most_played_tracks, 25) as row, i (i)}
-          <HorizontalScrollRow
-            items={row}
-            title={i === 0 ? 'Most played' : undefined}
-            ariaLabel="Most played row {i + 1}"
-          >
-            {#snippet item(track: import('$lib/api/types').TrackRef, idx: number)}
-              <CompactTrackCard
-                {track}
-                sectionTracks={row}
-                index={idx}
-              />
-            {/snippet}
-          </HorizontalScrollRow>
-        {/each}
+        <HorizontalScrollRow
+          rows={chunk(data.most_played_tracks, 25)}
+          title="Most played"
+          ariaLabel="Most played"
+        >
+          {#snippet item(track: import('$lib/api/types').TrackRef, globalIdx: number)}
+            <CompactTrackCard
+              {track}
+              sectionTracks={data.most_played_tracks}
+              index={globalIdx}
+            />
+          {/snippet}
+        </HorizontalScrollRow>
       {/if}
     </section>
 
@@ -118,7 +116,7 @@
         <p class="text-text-secondary">No recent plays.</p>
       {:else}
         <HorizontalScrollRow
-          items={data.last_played_artists}
+          rows={[data.last_played_artists]}
           title="Last played"
           ariaLabel="Last played artists"
         >