library: address artist art review findings

Cap the resolver at four covers, re-rank after deduplication so duplicate covers do not consume the grid budget, carry a thumbnail per fallback step, and advance to the grid when both the full image and its thumbnail fail. Negative-cache failed provider-image fetches per artist URL, clear materialized downloaded covers when all downloads are removed, and drop redundant plumbing.

app/src/test/kotlin/com/subtracks/data/db/LibraryDaoTest.kt

@@ -682,6 +682,27 @@ class LibraryDaoTest {
             assertEquals(listOf("art-2", "art-1"), dao.artistOnce(sourceId, "ar-1")!!.downloadedCoverArts)
         }
 
+    @Test
+    fun artistArtDeduplicatesCoversBeforeApplyingTheFourCoverBudget() =
+        runTest {
+            val sourceId = source()
+            val dao = db.libraryDao()
+            dao.upsertArtists(listOf(artist(sourceId, "ar-1", "Artist", albumCount = 6)))
+            dao.upsertAlbums(
+                listOf("A", "A", "O", "B", "C", "D").mapIndexed { index, cover ->
+                    album(sourceId, "al-$index", "Album $index", year = 2021L - index, starred = null)
+                        .copy(artistId = "ar-1", coverArt = cover)
+                },
+            )
+
+            dao.recomputeArtistArt(sourceId)
+
+            assertEquals(
+                listOf("A", "O", "B", "C"),
+                dao.artistOnce(sourceId, "ar-1")!!.coverArts,
+            )
+        }
+
     @Test
     fun artistArtMaterializationUsesTheCreditIndexes() =
         runTest {

app/src/test/kotlin/com/subtracks/data/repo/DownloadRepositoryTest.kt

@@ -346,7 +346,10 @@ class DownloadRepositoryTest {
         runTest {
             seedLibrary()
             writeFile(1, "s1", "audio")
-            runBlocking { repository.download(1, "s1") }
+            runBlocking {
+                repository.download(1, "s1")
+                db.libraryDao().upsertArtists(listOf(artist(ARTIST_ART).copy(downloadedCoverArts = listOf(ALBUM_ART))))
+            }
             val id = engine.requests.single().first
 
             runBlocking { repository.removeSource(1) }
@@ -354,6 +357,13 @@ class DownloadRepositoryTest {
             assertTrue(engine.cancelled.contains(id))
             assertFalse(file(1, "s1").exists())
             assertTrue(allRows().isEmpty())
+            assertTrue(
+                db
+                    .libraryDao()
+                    .artistOnce(1, "ar1")!!
+                    .downloadedCoverArts
+                    .isEmpty(),
+            )
         }
 
     @Test

app/src/test/kotlin/com/subtracks/ui/AppScreenshotTest.kt

@@ -334,11 +334,14 @@ class AppScreenshotTest {
                         ),
                     art = CoverArtRef("art-al-kid-a", "test:art-al-kid-a"),
                     artThumbnail = CoverArtRef("art-al-kid-a", "test:art-al-kid-a"),
-                    artCovers =
-                        Fixtures.albums
-                            .take(3)
-                            .mapNotNull { it.coverArt }
-                            .map { CoverArtRef(it, "test:$it") },
+                    heroArt =
+                        ArtistArt(
+                            covers =
+                                Fixtures.albums
+                                    .take(3)
+                                    .mapNotNull { it.coverArt }
+                                    .map { CoverArtRef(it, "test:$it") },
+                        ),
                     artwork = artworkColorsFromSeed(Color.rgb(120, 80, 200)),
                     coverArt = { id, _ -> id?.let { CoverArtRef(it, "test:$it") } },
                     onBack = {},

app/src/test/kotlin/com/subtracks/ui/components/ArtistArtTest.kt

@@ -76,8 +76,16 @@ class ArtistArtTest {
         }
         val artistImage: (String, String?) -> CoverArtRef? = { _, _ -> null }
 
-        resolveArtistArt(artist(coverArts = listOf("a")), coverArt, artistImage, offline = false, forIcon = false)
-        assertEquals(listOf(false), thumbnails)
+        val single =
+            resolveArtistArt(
+                artist(coverArts = listOf("a")),
+                coverArt,
+                artistImage,
+                offline = false,
+                forIcon = false,
+            )
+        assertEquals(listOf(true, false), thumbnails)
+        assertEquals("a", single.thumbnail?.url)
 
         thumbnails.clear()
         resolveArtistArt(artist(coverArts = listOf("a", "b")), coverArt, artistImage, offline = false, forIcon = false)