fix(clients): never leave cover tiles blank — shared web <Cover> + Android Coil placeholder/error

Cover tiles (worst in the "You might like" home row, which surfaces
unplayed items whose art is often not yet backfilled) sat empty while
loading and stayed blank on a 404. The server returns a fast 404; the
gap was missing client-side loading/fallback states.

Web: new shared Cover.svelte owns the loading placeholder + onerror
fallback (static cover, or Disc3 for artists). AlbumCard, ArtistCard and
CompactTrackCard now reuse it instead of three hand-rolled <img> tags
that disagreed on fallback handling — notably ArtistCard had no onerror.

Android: ServerImage tracks Coil's load state so the per-caller fallback
doubles as a placeholder (loading) and an error state (404 / unreachable),
instead of only guarding the null-URL case. All five call sites pass an
explicit size modifier, so the new Box wrapper is layout-safe.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

android/app/src/main/java/com/fabledsword/minstrel/shared/widgets/ServerImage.kt

@@ -1,15 +1,25 @@
 package com.fabledsword.minstrel.shared.widgets
 
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.layout.ContentScale
 import coil3.compose.AsyncImage
+import coil3.compose.AsyncImagePainter
 import com.fabledsword.minstrel.shared.resolveServerUrl
 
 /**
  * Renders a server-hosted image, resolving relative URLs centrally so
  * every cover surface loads consistently. Shows [fallback] when the URL
- * is blank or unresolvable.
+ * is blank/unresolvable, while the image is still loading, and when the
+ * load fails — so a tile is never left blank (e.g. art not yet backfilled,
+ * which the "You might like" row hits often).
  */
 @Composable
 fun ServerImage(
@@ -22,12 +32,26 @@ fun ServerImage(
     val resolved = resolveServerUrl(url)
     if (resolved == null) {
         fallback()
-    } else {
+        return
+    }
+    // Track Coil's load state so the fallback doubles as a placeholder
+    // (loading) and an error state (404 / unreachable) — not just a
+    // null-URL guard, which left present-but-failing URLs blank.
+    var state by remember(resolved) {
+        mutableStateOf<AsyncImagePainter.State>(AsyncImagePainter.State.Empty)
+    }
+    Box(modifier = modifier, contentAlignment = Alignment.Center) {
         AsyncImage(
             model = resolved,
             contentDescription = contentDescription,
-            modifier = modifier,
+            modifier = Modifier.fillMaxSize(),
             contentScale = contentScale,
+            onState = { state = it },
         )
+        if (state is AsyncImagePainter.State.Loading ||
+            state is AsyncImagePainter.State.Error
+        ) {
+            fallback()
+        }
     }
 }

web/src/lib/components/AlbumCard.svelte

@@ -1,18 +1,14 @@
 <script lang="ts">
   import type { AlbumRef, AlbumDetail } from '$lib/api/types';
-  import { FALLBACK_COVER } from '$lib/media/covers';
   import { api } from '$lib/api/client';
   import { enqueueTracks, playQueue } from '$lib/player/store.svelte';
   import { Play } from 'lucide-svelte';
   import AlbumMenu from './AlbumMenu.svelte';
   import CardActionCluster from './CardActionCluster.svelte';
+  import Cover from './Cover.svelte';
 
   let { album }: { album: AlbumRef } = $props();
 
-  function onImgError(e: Event) {
-    (e.currentTarget as HTMLImageElement).src = FALLBACK_COVER;
-  }
-
   async function onAddClick(e: MouseEvent) {
     e.preventDefault();
     e.stopPropagation();
@@ -38,12 +34,9 @@
              shadow-sm transition-all duration-150
              group-hover:shadow-lg group-hover:ring-1 group-hover:ring-accent/40"
     >
-      <img
+      <Cover
         src={album.cover_url}
-        alt=""
-        class="h-full w-full object-cover transition-transform group-hover:scale-[1.03]"
-        loading="lazy"
-        onerror={onImgError}
+        class="transition-transform group-hover:scale-[1.03]"
       />
       <button
         type="button"

web/src/lib/components/ArtistCard.svelte

@@ -2,9 +2,10 @@
   import type { ArtistRef, TrackRef } from '$lib/api/types';
   import { api } from '$lib/api/client';
   import { playQueue, enqueueTracks } from '$lib/player/store.svelte';
-  import { Disc3, Play } from 'lucide-svelte';
+  import { Play } from 'lucide-svelte';
   import ArtistMenu from './ArtistMenu.svelte';
   import CardActionCluster from './CardActionCluster.svelte';
+  import Cover from './Cover.svelte';
   import { listArtistTracks } from '$lib/api/artists';
 
   let { artist }: { artist: ArtistRef } = $props();
@@ -48,18 +49,12 @@
     class="block rounded focus-visible:ring-2 focus-visible:ring-accent"
   >
     <div class="art-wrap relative mx-auto aspect-square w-full overflow-hidden rounded-full bg-surface-hover">
-      {#if artist.cover_url}
-        <img
+      <Cover
         src={artist.cover_url}
-          alt=""
-          class="h-full w-full object-cover transition-transform group-hover:scale-[1.03]"
-          loading="lazy"
+        shape="round"
+        fallback="artist"
+        class="transition-transform group-hover:scale-[1.03]"
       />
-      {:else}
-        <div class="flex h-full w-full items-center justify-center">
-          <Disc3 strokeWidth={1} class="h-4/5 w-4/5 text-text-muted" />
-        </div>
-      {/if}
       <button
         type="button"
         aria-label={`Play ${artist.name}`}

web/src/lib/components/CompactTrackCard.svelte

@@ -2,9 +2,10 @@
   import { Plus } from 'lucide-svelte';
   import type { TrackRef } from '$lib/api/types';
   import { playQueue, enqueueTrack } from '$lib/player/store.svelte';
-  import { FALLBACK_COVER, coverUrl } from '$lib/media/covers';
+  import { coverUrl } from '$lib/media/covers';
   import TrackMenu from './TrackMenu.svelte';
   import LikeButton from './LikeButton.svelte';
+  import Cover from './Cover.svelte';
 
   // Horizontal compact track row — cover thumb on the left, title +
   // artist on the right. Mirrors Android's CompactTrackTile so the
@@ -23,10 +24,6 @@
 
   const cover = $derived(coverUrl(track.album_id));
 
-  function onImgError(e: Event) {
-    (e.currentTarget as HTMLImageElement).src = FALLBACK_COVER;
-  }
-
   function onClick() {
     playQueue(sectionTracks, index);
   }
@@ -47,13 +44,7 @@
            hover:bg-surface-hover focus-visible:ring-2 focus-visible:ring-accent"
   >
     <div class="h-12 w-12 flex-shrink-0 overflow-hidden rounded bg-surface-hover">
-      <img
-        src={cover}
-        alt=""
-        class="h-full w-full object-cover"
-        loading="lazy"
-        onerror={onImgError}
-      />
+      <Cover src={cover} />
     </div>
     <div class="min-w-0 flex-1">
       <div class="truncate text-sm font-medium text-text-primary">{track.title}</div>

web/src/lib/components/Cover.svelte

@@ -0,0 +1,66 @@
+<script lang="ts">
+  import { FALLBACK_COVER } from '$lib/media/covers';
+  import { Disc3 } from 'lucide-svelte';
+
+  // Shared cover-artwork renderer. The web counterpart of Android's
+  // CoverTile/ServerImage: one place that owns the loading placeholder and
+  // the error fallback so no card sits blank while art loads or 404s (the
+  // "You might like" row surfaces unplayed items whose art is often not yet
+  // backfilled). Replaces the three hand-rolled <img> tags that previously
+  // disagreed on fallback handling.
+  let {
+    src,
+    alt = '',
+    shape = 'square',
+    fallback = 'image',
+    class: klass = ''
+  }: {
+    src: string | undefined;
+    alt?: string;
+    // 'round' clips to a circle (artist avatars); 'square' leaves clipping
+    // to the parent so existing rounded-md / rounded corners still apply.
+    shape?: 'square' | 'round';
+    // 'artist' degrades to a Disc3 icon; 'image' to the static placeholder
+    // cover. A null/empty src is treated the same as a failed load.
+    fallback?: 'image' | 'artist';
+    class?: string;
+  } = $props();
+
+  // Per-image lifecycle. Reset when src changes so a reused card (virtualized
+  // list, client-side nav) never keeps a stale 'loaded'/'failed'.
+  let loaded = $state(false);
+  let failed = $state(false);
+  $effect(() => {
+    void src;
+    loaded = false;
+    failed = false;
+  });
+
+  const useIcon = $derived(fallback === 'artist' && (failed || !src));
+  // On failure for the image fallback, swap to the static placeholder asset.
+  // src doesn't change on the second error, so there's no reload loop.
+  const imgSrc = $derived(failed ? FALLBACK_COVER : src);
+</script>
+
+<div
+  class="relative h-full w-full overflow-hidden bg-surface-hover {shape === 'round'
+    ? 'rounded-full'
+    : ''}"
+>
+  {#if useIcon}
+    <div class="flex h-full w-full items-center justify-center">
+      <Disc3 strokeWidth={1} class="h-4/5 w-4/5 text-text-muted" />
+    </div>
+  {:else if imgSrc}
+    <img
+      src={imgSrc}
+      {alt}
+      class="h-full w-full object-cover transition-opacity duration-200 {loaded
+        ? 'opacity-100'
+        : 'opacity-0'} {klass}"
+      loading="lazy"
+      onload={() => (loaded = true)}
+      onerror={() => (failed = true)}
+    />
+  {/if}
+</div>