fix slider + list bugs

modules/astra-library-scanner/android/src/androidTest/java/expo/modules/astralibraryscanner/data/RoomLibraryRepositoryTest.kt

@@ -381,6 +381,95 @@ class RoomLibraryRepositoryTest {
     assertTrue(first.map { it.path }.intersect(second.map { it.path }.toSet()).isEmpty())
   }
 
+  /**
+   * Walking backwards has to reproduce the forward ordering exactly — an off-by-one in
+   * the reversed tie-break tuple would either duplicate a row or silently skip one when
+   * the list refills upwards after an A-Z jump.
+   */
+  @Test
+  fun backwardTitlePagesMirrorForwardPages() = runBlocking {
+    publish("g1", seedAlphabet())
+    val dao = catalog.catalogDao()
+
+    val forward = mutableListOf<ActiveTrackView>()
+    var afterKey: String? = null
+    var afterPath = ""
+    while (true) {
+      val page = dao.getTitlePage(afterKey, afterPath, 40)
+      if (page.isEmpty()) break
+      forward += page
+      afterKey = page.last().titleSortKey
+      afterPath = page.last().path
+    }
+    assertEquals(ALPHABET_SEED_SIZE, forward.size)
+
+    val backward = mutableListOf<ActiveTrackView>()
+    var beforeKey = forward.last().titleSortKey
+    var beforePath = forward.last().path
+    while (true) {
+      val page = dao.getTitlePageBefore(beforeKey, beforePath, 40)
+      if (page.isEmpty()) break
+      backward += page
+      beforeKey = page.last().titleSortKey
+      beforePath = page.last().path
+    }
+    // Backward pages are exclusive of the anchor row and come back descending.
+    assertEquals(
+      forward.dropLast(1).map { it.path }.reversed(),
+      backward.map { it.path },
+    )
+    // Nothing above the very first row.
+    assertTrue(dao.getTitlePageBefore(forward.first().titleSortKey, forward.first().path, 40).isEmpty())
+  }
+
+  /**
+   * The exact shape a rail jump uses: a section anchor carries only the leading sort key
+   * with an empty path tie-break, so the forward page starts at the letter and the
+   * backward page must be the slice immediately above it — no overlap, no gap.
+   */
+  @Test
+  fun sectionAnchorSplitsCatalogWithoutOverlapOrGap() = runBlocking {
+    publish("g1", seedAlphabet())
+    val dao = catalog.catalogDao()
+
+    val all = mutableListOf<ActiveTrackView>()
+    var afterKey: String? = null
+    var afterPath = ""
+    while (true) {
+      val page = dao.getTitlePage(afterKey, afterPath, 100)
+      if (page.isEmpty()) break
+      all += page
+      afterKey = page.last().titleSortKey
+      afterPath = page.last().path
+    }
+
+    val anchor = dao.getTitleSectionAnchors().first { it.sectionLabel == "F" }
+    val at = dao.getTitlePage(anchor.sortKey, "", 40)
+    val above = dao.getTitlePageBefore(anchor.sortKey, "", 40)
+
+    assertEquals("F", SortKeys.sectionLabel(at.first().title))
+    assertTrue(above.all { SortKeys.sectionLabel(it.title) != "F" })
+
+    val anchorIndex = all.indexOfFirst { it.path == at.first().path }
+    assertEquals(40, above.size)
+    assertEquals(
+      all.subList(anchorIndex - above.size, anchorIndex).map { it.path },
+      above.reversed().map { it.path },
+    )
+  }
+
+  /** 10 tracks under each of A-Z, so every section has rows above and below it. */
+  private fun seedAlphabet(): List<TrackEntity> =
+    (0 until ALPHABET_SEED_SIZE).map { index ->
+      val letter = 'A' + (index / 10)
+      track(
+        generation = "g1",
+        index = index,
+        title = "$letter${"%03d".format(index)} Song",
+        path = "content://track/$index.flac",
+      )
+    }
+
   private suspend fun publish(
     generation: String,
     tracks: List<TrackEntity>,
@@ -442,4 +531,9 @@ class RoomLibraryRepositoryTest {
     trackSort = index,
     sectionLabel = SortKeys.sectionLabel(title),
   )
+
+  private companion object {
+    /** 26 letters x 10 tracks. */
+    const val ALPHABET_SEED_SIZE = 260
+  }
 }

modules/astra-library-scanner/android/src/main/java/expo/modules/astralibraryscanner/AstraLibraryDataModule.kt

@@ -90,6 +90,18 @@ class AstraLibraryDataModule : Module() {
       }
     }
 
+    AsyncFunction("getTrackPageBefore") Coroutine {
+        sort: String,
+        cursor: String?,
+        limit: Int,
+      ->
+      try {
+        repository().getTrackPageBefore(sort, cursor, limit)
+      } catch (_: StaleRevisionException) {
+        mapOf("error" to "STALE_REVISION")
+      }
+    }
+
     AsyncFunction("getTrack") Coroutine { path: String ->
       repository().getTrack(path)
     }
@@ -367,6 +379,19 @@ class AstraLibraryDataModule : Module() {
       }
     }
 
+    AsyncFunction("getAlbumPageBefore") Coroutine {
+        sort: String,
+        includeSingles: Boolean,
+        cursor: String?,
+        limit: Int,
+      ->
+      try {
+        repository().getAlbumPageBefore(sort, includeSingles, cursor, limit)
+      } catch (_: StaleRevisionException) {
+        mapOf("error" to "STALE_REVISION")
+      }
+    }
+
     AsyncFunction("getArtistPage") Coroutine {
         sort: String,
         groupingMode: String,
@@ -381,6 +406,20 @@ class AstraLibraryDataModule : Module() {
       }
     }
 
+    AsyncFunction("getArtistPageBefore") Coroutine {
+        sort: String,
+        groupingMode: String,
+        includeCollaborations: Boolean,
+        cursor: String?,
+        limit: Int,
+      ->
+      try {
+        repository().getArtistPageBefore(sort, groupingMode, includeCollaborations, cursor, limit)
+      } catch (_: StaleRevisionException) {
+        mapOf("error" to "STALE_REVISION")
+      }
+    }
+
     AsyncFunction("getAlbumDetail") Coroutine { albumKey: String, cursor: String?, limit: Int ->
       try {
         repository().getAlbumDetail(albumKey, cursor, limit)

modules/astra-library-scanner/android/src/main/java/expo/modules/astralibraryscanner/data/AstraLibraryRepository.kt

@@ -596,7 +596,71 @@ class AstraLibraryRepository private constructor(
         limit = limit,
       )
     }
-    val next = rows.lastOrNull()?.let { row ->
+    val next = rows.lastOrNull()?.let { row -> trackCursor(revision, sort, row).encode() }
+    mapOf(
+      "items" to rows.map(ActiveTrackView::toBridgeMap),
+      "nextCursor" to next,
+      "previousCursor" to null,
+      "totalCount" to dao.countActiveTracks().toDouble(),
+      "catalogRevision" to revision.toString(),
+    )
+  }
+
+  /**
+   * The page immediately *above* [cursorRaw] — the backward twin of [getTrackPage].
+   * An A-Z rail jump drops the list into the middle of the catalog; this is what the
+   * rows above it are fetched with when the user scrolls back up. Items come back
+   * ascending, like every other page.
+   *
+   * `previousCursor` is non-null only on a full page: a short one means we walked off
+   * the head of the catalog, so the caller knows to stop asking.
+   *
+   * Only the sorts the rail is offered for (`title`, `artist`) can be walked backwards;
+   * anything else returns an empty page.
+   */
+  suspend fun getTrackPageBefore(
+    sort: String,
+    cursorRaw: String?,
+    requestedLimit: Int,
+  ): Map<String, Any?> = withCatalogRecovery { database ->
+    initialize()
+    val dao = database.catalogDao()
+    val revision = dao.getRevision()
+    val cursor = validateCursor(cursorRaw, revision, "tracks:$sort")
+    val limit = requestedLimit.coerceIn(1, MAX_PAGE_SIZE)
+    val descending = when {
+      cursor == null -> emptyList()
+      sort == "artist" -> dao.getArtistOrderPageBefore(
+        beforeArtistKey = cursor.text1.orEmpty(),
+        beforeAlbumKey = cursor.text2.orEmpty(),
+        beforeDisc = cursor.number1?.toInt() ?: 0,
+        beforeTrack = cursor.number2?.toInt() ?: 0,
+        beforeTitleKey = cursorTitleKey(cursor),
+        beforePath = cursorPath(cursor),
+        limit = limit,
+      )
+      sort == "title" -> dao.getTitlePageBefore(
+        beforeTitleKey = cursor.text1.orEmpty(),
+        beforePath = cursor.text2.orEmpty(),
+        limit = limit,
+      )
+      else -> emptyList()
+    }
+    // The DESC result's last row is the topmost one — the cursor for the page above this one.
+    val previous = descending.takeIf { it.size == limit }
+      ?.lastOrNull()
+      ?.let { row -> trackCursor(revision, sort, row).encode() }
+    mapOf(
+      "items" to descending.reversed().map(ActiveTrackView::toBridgeMap),
+      "nextCursor" to null,
+      "previousCursor" to previous,
+      "totalCount" to dao.countActiveTracks().toDouble(),
+      "catalogRevision" to revision.toString(),
+    )
+  }
+
+  /** Shared by the forward and backward track pages so the two can never disagree. */
+  private fun trackCursor(revision: Long, sort: String, row: ActiveTrackView): TrackPageCursor =
     when (sort) {
       "artist" -> TrackPageCursor(
         revision = revision,
@@ -627,15 +691,6 @@ class AstraLibraryRepository private constructor(
         text1 = row.titleSortKey,
         text2 = row.path,
       )
-      }.encode()
-    }
-    mapOf(
-      "items" to rows.map(ActiveTrackView::toBridgeMap),
-      "nextCursor" to next,
-      "previousCursor" to null,
-      "totalCount" to dao.countActiveTracks().toDouble(),
-      "catalogRevision" to revision.toString(),
-    )
     }
 
   suspend fun getTrack(path: String): Map<String, Any?>? =
@@ -1674,7 +1729,66 @@ class AstraLibraryRepository private constructor(
         limit,
       )
     }
-    val next = rows.lastOrNull()?.let { row ->
+    val next = rows.lastOrNull()?.let { row -> albumCursor(revision, kind, sort, row).encode() }
+    mapOf(
+      "items" to rows.map(AlbumSummaryEntity::toBridgeMap),
+      "nextCursor" to next,
+      "previousCursor" to null,
+      "totalCount" to dao.countAlbums(revision, includeSingles).toDouble(),
+      "catalogRevision" to revision.toString(),
+    )
+  }
+
+  /** Backward twin of [getAlbumPage]; see [getTrackPageBefore] for the contract. */
+  suspend fun getAlbumPageBefore(
+    sort: String,
+    includeSingles: Boolean,
+    cursorRaw: String?,
+    requestedLimit: Int,
+  ): Map<String, Any?> = withCatalogRecovery { database ->
+    val dao = database.catalogDao()
+    val revision = dao.getRevision()
+    val kind = "albums:$sort:${if (includeSingles) 1 else 0}"
+    val cursor = validateCursor(cursorRaw, revision, kind)
+    val limit = requestedLimit.coerceIn(1, MAX_PAGE_SIZE)
+    val descending = when {
+      cursor == null -> emptyList()
+      sort == "artist" -> dao.getAlbumArtistPageBefore(
+        revision,
+        includeSingles,
+        cursor.text1.orEmpty(),
+        cursor.text2.orEmpty(),
+        cursor.text3.orEmpty(),
+        limit,
+      )
+      sort == "name" -> dao.getAlbumNamePageBefore(
+        revision,
+        includeSingles,
+        cursor.text1.orEmpty(),
+        cursor.text2.orEmpty(),
+        limit,
+      )
+      else -> emptyList()
+    }
+    val previous = descending.takeIf { it.size == limit }
+      ?.lastOrNull()
+      ?.let { row -> albumCursor(revision, kind, sort, row).encode() }
+    mapOf(
+      "items" to descending.reversed().map(AlbumSummaryEntity::toBridgeMap),
+      "nextCursor" to null,
+      "previousCursor" to previous,
+      "totalCount" to dao.countAlbums(revision, includeSingles).toDouble(),
+      "catalogRevision" to revision.toString(),
+    )
+  }
+
+  /** Shared by the forward and backward album pages so the two can never disagree. */
+  private fun albumCursor(
+    revision: Long,
+    kind: String,
+    sort: String,
+    row: AlbumSummaryEntity,
+  ): TrackPageCursor =
     when (sort) {
       "artist" -> TrackPageCursor(
         revision,
@@ -1702,15 +1816,6 @@ class AstraLibraryRepository private constructor(
         text1 = row.nameSortKey,
         text2 = row.identityKey,
       )
-      }.encode()
-    }
-    mapOf(
-      "items" to rows.map(AlbumSummaryEntity::toBridgeMap),
-      "nextCursor" to next,
-      "previousCursor" to null,
-      "totalCount" to dao.countAlbums(revision, includeSingles).toDouble(),
-      "catalogRevision" to revision.toString(),
-    )
     }
 
   suspend fun getArtistPage(
@@ -1746,15 +1851,7 @@ class AstraLibraryRepository private constructor(
         limit,
       )
     }
-    val next = rows.lastOrNull()?.let { row ->
-      TrackPageCursor(
-        revision,
-        kind,
-        text1 = row.nameSortKey,
-        text2 = row.artistKey,
-        number1 = if (sort == "track_count") row.trackCount else null,
-      ).encode()
-    }
+    val next = rows.lastOrNull()?.let { row -> artistCursor(revision, kind, sort, row).encode() }
     mapOf(
       "items" to rows.map(ArtistSummaryEntity::toBridgeMap),
       "nextCursor" to next,
@@ -1764,6 +1861,59 @@ class AstraLibraryRepository private constructor(
     )
   }
 
+  /** Backward twin of [getArtistPage]; see [getTrackPageBefore] for the contract. */
+  suspend fun getArtistPageBefore(
+    sort: String,
+    groupingMode: String,
+    includeCollaborations: Boolean,
+    cursorRaw: String?,
+    requestedLimit: Int,
+  ): Map<String, Any?> = withCatalogRecovery { database ->
+    val dao = database.catalogDao()
+    val revision = dao.getRevision()
+    val mode = if (groupingMode == "fileTags") "fileTags" else "astra"
+    val kind = "artists:$sort:$mode:${if (includeCollaborations) 1 else 0}"
+    val cursor = validateCursor(cursorRaw, revision, kind)
+    val limit = requestedLimit.coerceIn(1, MAX_PAGE_SIZE)
+    val descending = if (cursor == null || sort == "track_count") {
+      emptyList()
+    } else {
+      dao.getArtistNamePageBefore(
+        revision,
+        mode,
+        includeCollaborations,
+        cursor.text1.orEmpty(),
+        cursor.text2.orEmpty(),
+        limit,
+      )
+    }
+    val previous = descending.takeIf { it.size == limit }
+      ?.lastOrNull()
+      ?.let { row -> artistCursor(revision, kind, sort, row).encode() }
+    mapOf(
+      "items" to descending.reversed().map(ArtistSummaryEntity::toBridgeMap),
+      "nextCursor" to null,
+      "previousCursor" to previous,
+      "totalCount" to dao.countArtists(revision, mode, includeCollaborations).toDouble(),
+      "catalogRevision" to revision.toString(),
+    )
+  }
+
+  /** Shared by the forward and backward artist pages so the two can never disagree. */
+  private fun artistCursor(
+    revision: Long,
+    kind: String,
+    sort: String,
+    row: ArtistSummaryEntity,
+  ): TrackPageCursor =
+    TrackPageCursor(
+      revision,
+      kind,
+      text1 = row.nameSortKey,
+      text2 = row.artistKey,
+      number1 = if (sort == "track_count") row.trackCount else null,
+    )
+
   suspend fun getAlbumDetail(
     albumKey: String,
     cursorRaw: String?,

modules/astra-library-scanner/android/src/main/java/expo/modules/astralibraryscanner/data/CatalogDatabase.kt

@@ -360,6 +360,26 @@ interface CatalogDao {
     limit: Int,
   ): List<ActiveTrackView>
 
+  /**
+   * Mirror of [getTitlePage] walking backwards. Rows come out DESC — the caller
+   * reverses them so `items` is ascending like every other page. Backward paging
+   * always has a cursor (there is nothing before the head), so no NULL branch.
+   */
+  @Query(
+    """
+      SELECT * FROM active_tracks
+      WHERE title_sort_key < :beforeTitleKey
+        OR (title_sort_key = :beforeTitleKey AND path < :beforePath)
+      ORDER BY title_sort_key DESC, path DESC
+      LIMIT :limit
+    """,
+  )
+  suspend fun getTitlePageBefore(
+    beforeTitleKey: String,
+    beforePath: String,
+    limit: Int,
+  ): List<ActiveTrackView>
+
   @Query(
     """
       SELECT * FROM active_tracks
@@ -387,6 +407,34 @@ interface CatalogDao {
     limit: Int,
   ): List<ActiveTrackView>
 
+  /** Mirror of [getArtistOrderPage] walking backwards; rows come out DESC. */
+  @Query(
+    """
+      SELECT * FROM active_tracks
+      WHERE artist_sort_key < :beforeArtistKey
+        OR (artist_sort_key = :beforeArtistKey AND album_sort_key < :beforeAlbumKey)
+        OR (artist_sort_key = :beforeArtistKey AND album_sort_key = :beforeAlbumKey AND disc_sort < :beforeDisc)
+        OR (artist_sort_key = :beforeArtistKey AND album_sort_key = :beforeAlbumKey AND disc_sort = :beforeDisc
+            AND track_sort < :beforeTrack)
+        OR (artist_sort_key = :beforeArtistKey AND album_sort_key = :beforeAlbumKey AND disc_sort = :beforeDisc
+            AND track_sort = :beforeTrack AND title_sort_key < :beforeTitleKey)
+        OR (artist_sort_key = :beforeArtistKey AND album_sort_key = :beforeAlbumKey AND disc_sort = :beforeDisc
+            AND track_sort = :beforeTrack AND title_sort_key = :beforeTitleKey AND path < :beforePath)
+      ORDER BY artist_sort_key DESC, album_sort_key DESC, disc_sort DESC, track_sort DESC,
+        title_sort_key DESC, path DESC
+      LIMIT :limit
+    """,
+  )
+  suspend fun getArtistOrderPageBefore(
+    beforeArtistKey: String,
+    beforeAlbumKey: String,
+    beforeDisc: Int,
+    beforeTrack: Int,
+    beforeTitleKey: String,
+    beforePath: String,
+    limit: Int,
+  ): List<ActiveTrackView>
+
   @Query(
     """
       SELECT * FROM active_tracks
@@ -543,6 +591,26 @@ interface CatalogDao {
     limit: Int,
   ): List<AlbumSummaryEntity>
 
+  /** Mirror of [getAlbumNamePage] walking backwards; rows come out DESC. */
+  @Query(
+    """
+      SELECT * FROM album_summaries
+      WHERE revision = :revision
+        AND (:includeSingles OR is_single = 0)
+        AND (name_sort_key < :beforeKey
+          OR (name_sort_key = :beforeKey AND identity_key < :beforeId))
+      ORDER BY name_sort_key DESC, identity_key DESC
+      LIMIT :limit
+    """,
+  )
+  suspend fun getAlbumNamePageBefore(
+    revision: Long,
+    includeSingles: Boolean,
+    beforeKey: String,
+    beforeId: String,
+    limit: Int,
+  ): List<AlbumSummaryEntity>
+
   @Query(
     """
       SELECT * FROM album_summaries
@@ -566,6 +634,29 @@ interface CatalogDao {
     limit: Int,
   ): List<AlbumSummaryEntity>
 
+  /** Mirror of [getAlbumArtistPage] walking backwards; rows come out DESC. */
+  @Query(
+    """
+      SELECT * FROM album_summaries
+      WHERE revision = :revision
+        AND (:includeSingles OR is_single = 0)
+        AND (artist_sort_key < :beforeArtistKey
+          OR (artist_sort_key = :beforeArtistKey AND name_sort_key < :beforeNameKey)
+          OR (artist_sort_key = :beforeArtistKey AND name_sort_key = :beforeNameKey
+              AND identity_key < :beforeId))
+      ORDER BY artist_sort_key DESC, name_sort_key DESC, identity_key DESC
+      LIMIT :limit
+    """,
+  )
+  suspend fun getAlbumArtistPageBefore(
+    revision: Long,
+    includeSingles: Boolean,
+    beforeArtistKey: String,
+    beforeNameKey: String,
+    beforeId: String,
+    limit: Int,
+  ): List<AlbumSummaryEntity>
+
   @Query(
     """
       SELECT * FROM album_summaries
@@ -652,6 +743,28 @@ interface CatalogDao {
     limit: Int,
   ): List<ArtistSummaryEntity>
 
+  /** Mirror of [getArtistNamePage] walking backwards; rows come out DESC. */
+  @Query(
+    """
+      SELECT * FROM artist_summaries
+      WHERE revision = :revision
+        AND grouping_mode = :groupingMode
+        AND (:includeCollaborations OR is_collaboration = 0)
+        AND (name_sort_key < :beforeKey
+          OR (name_sort_key = :beforeKey AND artist_key < :beforeId))
+      ORDER BY name_sort_key DESC, artist_key DESC
+      LIMIT :limit
+    """,
+  )
+  suspend fun getArtistNamePageBefore(
+    revision: Long,
+    groupingMode: String,
+    includeCollaborations: Boolean,
+    beforeKey: String,
+    beforeId: String,
+    limit: Int,
+  ): List<ArtistSummaryEntity>
+
   @Query(
     """
       SELECT * FROM artist_summaries

modules/astra-library-scanner/index.ts

@@ -288,6 +288,16 @@ declare class AstraLibraryDataModuleType extends NativeModule<AstraLibraryDataEv
     cursor: string | null,
     limit: number
   ): Promise<NativePage<T>>;
+  /**
+   * The page immediately above `cursor` — how the lists refill upwards after an A-Z
+   * jump lands mid-catalog. Items come back ascending; `previousCursor` is null once
+   * there is nothing left above. Only the rail's sorts can be walked backwards.
+   */
+  getTrackPageBefore<T>(
+    sort: 'artist' | 'title',
+    cursor: string | null,
+    limit: number
+  ): Promise<NativePage<T>>;
   getTrack<T>(path: string): Promise<T | null>;
   getTrackLoudness(paths: string[]): Promise<NativeTrackLoudness[]>;
   setTrackLoudness(path: string, lufs: number | null, samplePeak: number | null): Promise<void>;
@@ -402,6 +412,13 @@ declare class AstraLibraryDataModuleType extends NativeModule<AstraLibraryDataEv
     cursor: string | null,
     limit: number
   ): Promise<NativePage<T>>;
+  /** Backward twin of `getAlbumPage`; see `getTrackPageBefore`. */
+  getAlbumPageBefore<T>(
+    sort: 'artist' | 'name',
+    includeSingles: boolean,
+    cursor: string | null,
+    limit: number
+  ): Promise<NativePage<T>>;
   getArtistPage<T>(
     sort: 'name' | 'track_count',
     groupingMode: 'astra' | 'fileTags',
@@ -409,6 +426,14 @@ declare class AstraLibraryDataModuleType extends NativeModule<AstraLibraryDataEv
     cursor: string | null,
     limit: number
   ): Promise<NativePage<T>>;
+  /** Backward twin of `getArtistPage`; see `getTrackPageBefore`. */
+  getArtistPageBefore<T>(
+    sort: 'name',
+    groupingMode: 'astra' | 'fileTags',
+    includeCollaborations: boolean,
+    cursor: string | null,
+    limit: number
+  ): Promise<NativePage<T>>;
   getAlbumDetail<T, S = Record<string, unknown>>(
     albumKey: string,
     cursor: string | null,

src/app/(tabs)/library/album/[key].tsx

@@ -112,7 +112,7 @@ export default function AlbumScreen() {
         onScroll={onScroll}
         scrollEventThrottle={scrollEventThrottle}
         onEndReached={() => void loadMore()}
-        onEndReachedThreshold={0.6}
+        onEndReachedThreshold={2}
         contentContainerStyle={{
           paddingTop: insets.top + expandedHeight,
           paddingHorizontal: spacing.lg,

src/app/(tabs)/library/artist/[name].tsx

@@ -221,6 +221,16 @@ export default function ArtistScreen() {
         renderItem={renderItem}
         onScroll={onScroll}
         scrollEventThrottle={scrollEventThrottle}
+        // This screen composes four paged sources into one list and had no paging
+        // trigger at all, so anything past the first page was unreachable. Each
+        // loadMore no-ops once its own cursor runs out.
+        onEndReached={() => {
+          void allPage.loadMore();
+          void songsPage.loadMore();
+          void appearancesPage.loadMore();
+          void albumsPage.loadMore();
+        }}
+        onEndReachedThreshold={2}
         contentContainerStyle={{
           paddingTop: insets.top + expandedHeight,
           paddingHorizontal: spacing.lg,

src/app/(tabs)/library/artist/[name]/albums.tsx

@@ -51,7 +51,7 @@ export default function ArtistAlbumsScreen() {
         keyExtractor={(album) => album.identity_key}
         showsVerticalScrollIndicator={false}
         onEndReached={() => void page.loadMore()}
-        onEndReachedThreshold={0.6}
+        onEndReachedThreshold={2}
         renderItem={({ item }) => (
           <View style={styles.gridCell}>
             <AlbumGridItem

src/app/(tabs)/library/artist/[name]/appearances.tsx

@@ -73,7 +73,7 @@ export default function ArtistAppearancesScreen() {
         keyExtractor={(track) => String(track.id)}
         showsVerticalScrollIndicator={false}
         onEndReached={() => void loadMore()}
-        onEndReachedThreshold={0.6}
+        onEndReachedThreshold={2}
         renderItem={({ item, index }) => (
           <TrackRow
             track={item}

src/app/(tabs)/library/artist/[name]/songs.tsx

@@ -73,7 +73,7 @@ export default function ArtistSongsScreen() {
         keyExtractor={(track) => String(track.id)}
         showsVerticalScrollIndicator={false}
         onEndReached={() => void loadMore()}
-        onEndReachedThreshold={0.6}
+        onEndReachedThreshold={2}
         renderItem={({ item, index }) => (
           <TrackRow
             track={item}

src/app/(tabs)/library/index.tsx

@@ -1,9 +1,12 @@
 import {
   useCallback,
+  useEffect,
   useMemo,
+  useRef,
   useState
 } from 'react';
 import {
+  ActivityIndicator,
   BackHandler,
   View,
   Pressable,
@@ -68,6 +71,14 @@ import type {
 const TRACK_SORT_OPTIONS: TrackSort[] = ['artist', 'title', 'recently_added', 'duration'];
 const ALBUM_SORT_OPTIONS: AlbumSort[] = ['artist', 'name', 'recently_added', 'year'];
 const ARTIST_SORT_OPTIONS: ArtistSort[] = ['name', 'track_count'];
+/** How long the finger has to settle on a rail letter before the list jumps. */
+const JUMP_DEBOUNCE_MS = 100;
+/**
+ * Screens of runway to keep ahead of the scroll. The old 0.6 was less than a fling
+ * covers before a page comes back, so the list hit a wall that looked like the end.
+ */
+const END_REACHED_THRESHOLD = 2;
+const START_REACHED_THRESHOLD = 0.5;
 
 export default function LibraryScreen() {
   const colors = useColors();
@@ -87,8 +98,15 @@ export default function LibraryScreen() {
   const loadNextTracks = useLibraryStore((s) => s.loadNextTracks);
   const loadNextAlbums = useLibraryStore((s) => s.loadNextAlbums);
   const loadNextArtists = useLibraryStore((s) => s.loadNextArtists);
+  const loadPreviousTracks = useLibraryStore((s) => s.loadPreviousTracks);
+  const loadPreviousAlbums = useLibraryStore((s) => s.loadPreviousAlbums);
+  const loadPreviousArtists = useLibraryStore((s) => s.loadPreviousArtists);
+  const trackNextCursor = useLibraryStore((s) => s.trackNextCursor);
+  const albumNextCursor = useLibraryStore((s) => s.albumNextCursor);
+  const artistNextCursor = useLibraryStore((s) => s.artistNextCursor);
   const sectionAnchors = useLibraryStore((s) => s.sectionAnchors);
   const sectionJumpRevision = useLibraryStore((s) => s.sectionJumpRevision);
+  const jumpAnchorIndex = useLibraryStore((s) => s.jumpAnchorIndex);
   const jumpToSection = useLibraryStore((s) => s.jumpToSection);
   const isScanning = useLibraryStore((s) => s.isScanning);
   const scanError = useLibraryStore((s) => s.scanError);
@@ -127,19 +145,64 @@ export default function LibraryScreen() {
   };
   const openSearch = () => openQuickSearch();
 
+  // Sits at the end of the loaded window whenever more pages exist, so a fling that
+  // outruns the loader stops on a spinner rather than on what looks like the end of
+  // the list. Gated on the cursor rather than on an in-flight flag so it does not
+  // blink between pages.
+  const listFooter = useMemo(
+    () => (
+      <View style={styles.listFooter}>
+        <ActivityIndicator size="small" color={colors.textTertiary} />
+      </View>
+    ),
+    [colors.textTertiary]
+  );
+
   const railVisible = sectionAnchors.length > 1;
   const railLetters = useMemo(
     () => new Set(sectionAnchors.map((entry) => entry.label)),
     [sectionAnchors]
   );
 
-  const jumpToLetter = (letter: string) => {
-    const anchor = sectionAnchors.find((entry) => entry.label === letter);
+  // A jump refills the window and remounts the list, so firing one per letter crossed
+  // made a fast scrub ~27 rebuilds. The bubble and haptic still track every letter
+  // (they live in the rail); only the jump itself waits for the finger to settle, and
+  // lifting off flushes it immediately.
+  const pendingJump = useRef<{ letter: string; timer: ReturnType<typeof setTimeout> } | null>(null);
+
+  const runJump = useCallback((letter: string) => {
+    const anchor = useLibraryStore.getState().sectionAnchors.find((entry) => entry.label === letter);
     if (!anchor) return;
     void jumpToSection(anchor.cursor).then((applied) => {
-      if (applied) scrollTop.setScrollAtTop(true);
+      // A jump usually lands with a page of rows above it, so the list is not at true
+      // top and pull-to-search must stay disarmed.
+      if (applied) scrollTop.setScrollAtTop(useLibraryStore.getState().jumpAnchorIndex === 0);
     });
+  }, [jumpToSection, scrollTop]);
+
+  const jumpToLetter = useCallback((letter: string) => {
+    if (pendingJump.current) clearTimeout(pendingJump.current.timer);
+    pendingJump.current = {
+      letter,
+      timer: setTimeout(() => {
+        pendingJump.current = null;
+        runJump(letter);
+      }, JUMP_DEBOUNCE_MS),
     };
+  }, [runJump]);
+
+  const flushJump = useCallback(() => {
+    const pending = pendingJump.current;
+    if (!pending) return;
+    clearTimeout(pending.timer);
+    pendingJump.current = null;
+    runJump(pending.letter);
+  }, [runJump]);
+
+  useEffect(() => () => {
+    if (pendingJump.current) clearTimeout(pendingJump.current.timer);
+    pendingJump.current = null;
+  }, []);
 
   // Multi-select (tracks view): long-press arms it, batch actions live in the
   // bottom bar, selection order follows the current display order.
@@ -303,8 +366,12 @@ export default function LibraryScreen() {
                   renderScrollComponent={PullSearchScrollView}
                   onScroll={scrollTop.onScroll}
                   scrollEventThrottle={scrollTop.scrollEventThrottle}
+                  initialScrollIndex={jumpAnchorIndex}
                   onEndReached={() => void loadNextAlbums()}
-                  onEndReachedThreshold={0.6}
+                  onEndReachedThreshold={END_REACHED_THRESHOLD}
+                  onStartReached={() => void loadPreviousAlbums()}
+                  onStartReachedThreshold={START_REACHED_THRESHOLD}
+                  ListFooterComponent={albumNextCursor ? listFooter : null}
                   renderItem={({ item }) => (
                     <View style={styles.gridCell}>
                       <AlbumGridItem
@@ -332,8 +399,12 @@ export default function LibraryScreen() {
                   renderScrollComponent={PullSearchScrollView}
                   onScroll={scrollTop.onScroll}
                   scrollEventThrottle={scrollTop.scrollEventThrottle}
+                  initialScrollIndex={jumpAnchorIndex}
                   onEndReached={() => void loadNextArtists()}
-                  onEndReachedThreshold={0.6}
+                  onEndReachedThreshold={END_REACHED_THRESHOLD}
+                  onStartReached={() => void loadPreviousArtists()}
+                  onStartReachedThreshold={START_REACHED_THRESHOLD}
+                  ListFooterComponent={artistNextCursor ? listFooter : null}
                   renderItem={({ item }) => (
                     <View style={styles.gridCell}>
                       <ArtistGridItem
@@ -360,8 +431,12 @@ export default function LibraryScreen() {
                   renderScrollComponent={PullSearchScrollView}
                   onScroll={scrollTop.onScroll}
                   scrollEventThrottle={scrollTop.scrollEventThrottle}
+                  initialScrollIndex={jumpAnchorIndex}
                   onEndReached={() => void loadNextTracks()}
-                  onEndReachedThreshold={0.6}
+                  onEndReachedThreshold={END_REACHED_THRESHOLD}
+                  onStartReached={() => void loadPreviousTracks()}
+                  onStartReachedThreshold={START_REACHED_THRESHOLD}
+                  ListFooterComponent={trackNextCursor ? listFooter : null}
                   extraData={selectMode ? selectedIds : undefined}
                   renderItem={({ item, index }) => (
                     <TrackRow
@@ -393,7 +468,11 @@ export default function LibraryScreen() {
               ) : null}
 
               {railVisible ? (
-                <AlphabetRail activeLetters={railLetters} onJumpToLetter={jumpToLetter} />
+                <AlphabetRail
+                  activeLetters={railLetters}
+                  onJumpToLetter={jumpToLetter}
+                  onScrubEnd={flushJump}
+                />
               ) : null}
             </View>
           </>
@@ -481,4 +560,8 @@ const styles = StyleSheet.create({
   listArea: {
     flex: 1,
   },
+  listFooter: {
+    paddingVertical: spacing.lg,
+    alignItems: 'center',
+  },
 });

src/app/(tabs)/library/playlist/[id].tsx

@@ -284,7 +284,7 @@ export default function PlaylistScreen() {
         onEndReached={() => {
           if (!isFavorites) void loadNextEntries();
         }}
-        onEndReachedThreshold={0.6}
+        onEndReachedThreshold={2}
         contentContainerStyle={{
           paddingTop: insets.top + expandedHeight,
           paddingHorizontal: spacing.lg,

src/components/library/AlphabetRail.tsx

@@ -20,6 +20,12 @@ interface AlphabetRailProps {
   /** Letters present in the current list — the rest render dimmed. */
   activeLetters: ReadonlySet<string>;
   onJumpToLetter: (letter: string) => void;
+  /**
+   * Fired when the finger lifts. The screen debounces `onJumpToLetter` so a fast
+   * scrub does not rebuild the list once per letter crossed; this is its cue to
+   * commit the last letter immediately instead of waiting out the debounce.
+   */
+  onScrubEnd?: () => void;
 }
 
 /**
@@ -30,7 +36,7 @@ interface AlphabetRailProps {
  * changes on a letter-cross). Blocks the pull-to-search gesture so a scrub at
  * scroll-top never arms the search indicator.
  */
-export function AlphabetRail({ activeLetters, onJumpToLetter }: AlphabetRailProps) {
+export function AlphabetRail({ activeLetters, onJumpToLetter, onScrubEnd }: AlphabetRailProps) {
   const styles = useStyles();
   const pullSearchRef = usePullSearchGestureRef();
   const [scrubLetter, setScrubLetter] = useState<string | null>(null);
@@ -49,7 +55,10 @@ export function AlphabetRail({ activeLetters, onJumpToLetter }: AlphabetRailProp
     playHaptic('frequentStep');
     onJumpToLetter(letter);
   };
-  const endScrub = () => setScrubLetter(null);
+  const endScrub = () => {
+    setScrubLetter(null);
+    onScrubEnd?.();
+  };
 
   const pan = useMemo(() => {
     const gesture = Gesture.Pan()
@@ -89,7 +98,7 @@ export function AlphabetRail({ activeLetters, onJumpToLetter }: AlphabetRailProp
       });
     return pullSearchRef ? gesture.blocksExternalGesture(pullSearchRef) : gesture;
     // eslint-disable-next-line react-hooks/exhaustive-deps -- scrubTo/endScrub capture the latest props via render closure
-  }, [lastLetter, bubbleY, railTop, pullSearchRef, activeLetters, onJumpToLetter]);
+  }, [lastLetter, bubbleY, railTop, pullSearchRef, activeLetters, onJumpToLetter, onScrubEnd]);
 
   const bubbleStyle = useAnimatedStyle(() => ({
     transform: [{ translateY: bubbleY.value - BUBBLE_SIZE / 2 }],

src/library/nativePages.ts

@@ -4,8 +4,7 @@ import { normalizeKey } from '@/shared/library/albumGrouping';
 import type { ArtistGroupingMode } from '@/library/artistGrouping';
 import type { Album, Artist, DbTrack } from '@/types/library';
 
-const DETAIL_PAGE_SIZE = 100;
-const MAX_DETAIL_ITEMS = 500;
+const DETAIL_PAGE_SIZE = 200;
 
 export type NativeAlbumSummary = Album & { total_duration?: number };
 
@@ -17,12 +16,12 @@ interface PagedDetail<T, S> {
   loadMore: () => Promise<void>;
 }
 
+// Grows without a cap: trimming the head shrank content height mid-scroll, which
+// read as the list snapping to the bottom, and these lists have no way to page back
+// upwards. See the same note on appendWindow in libraryStore.
 function appendTracks(current: DbTrack[], incoming: DbTrack[]): DbTrack[] {
   const paths = new Set(current.map((track) => track.path));
-  const merged = [...current, ...incoming.filter((track) => !paths.has(track.path))];
-  return merged.length > MAX_DETAIL_ITEMS
-    ? merged.slice(merged.length - MAX_DETAIL_ITEMS)
-    : merged;
+  return [...current, ...incoming.filter((track) => !paths.has(track.path))];
 }
 
 export function useNativeAlbumDetail(albumKey: string): PagedDetail<DbTrack, NativeAlbumSummary> {
@@ -191,8 +190,7 @@ export function useNativeArtistAlbums(
       );
       setItems((current) => {
         const known = new Set(current.map((album) => album.identity_key));
-        const merged = [...current, ...page.items.filter((album) => !known.has(album.identity_key))];
-        return merged.slice(-MAX_DETAIL_ITEMS);
+        return [...current, ...page.items.filter((album) => !known.has(album.identity_key))];
       });
       setTotalCount(page.totalCount);
       setNextOffset(page.nextOffset);

src/stores/libraryStore.ts

@@ -26,8 +26,7 @@ const TRACK_SORT_KEY = 'library_track_sort';
 const ALBUM_SORT_KEY = 'library_album_sort';
 const ARTIST_SORT_KEY = 'library_artist_sort';
 const INCLUDE_COLLAB_ARTISTS_KEY = 'library_include_collab_artists';
-const PAGE_SIZE = 100;
-const MAX_WINDOW_ITEMS = PAGE_SIZE * 5;
+const PAGE_SIZE = 200;
 
 const VIEW_MODES: readonly ViewMode[] = ['tracks', 'albums', 'artists', 'playlists', 'folders'];
 
@@ -80,20 +79,32 @@ interface LibraryStore {
   artistSort: ArtistSort;
   includeCollabArtists: boolean;
   isScanning: boolean;
-  isPageLoading: boolean;
   scanProgress: ScanProgressState;
   scanError: string | null;
   trackNextCursor: string | null;
   albumNextCursor: string | null;
   artistNextCursor: string | null;
+  /** Non-null only after a rail jump left rows above the loaded window. */
+  trackPrevCursor: string | null;
+  albumPrevCursor: string | null;
+  artistPrevCursor: string | null;
   sectionAnchors: LibrarySectionAnchor[];
   sectionJumpRevision: number;
+  /**
+   * Where the jumped-to letter sits in the freshly built window — fed to the list's
+   * `initialScrollIndex` on the remount that `sectionJumpRevision` triggers, so the
+   * letter lands at the top with a page of rows already above it to scroll back into.
+   */
+  jumpAnchorIndex: number;
 
   initialize: () => Promise<void>;
   refresh: () => Promise<void>;
   loadNextTracks: () => Promise<void>;
   loadNextAlbums: () => Promise<void>;
   loadNextArtists: () => Promise<void>;
+  loadPreviousTracks: () => Promise<void>;
+  loadPreviousAlbums: () => Promise<void>;
+  loadPreviousArtists: () => Promise<void>;
   jumpToSection: (cursor: string) => Promise<boolean>;
   recordTrackPlayed: (path: string) => Promise<void>;
   recomputeArtists: () => void;
@@ -112,14 +123,44 @@ interface LibraryStore {
 let initPromise: Promise<void> | null = null;
 let nativeSubscriptionsInstalled = false;
 
+// These grow without a cap on purpose. A sliding window that dropped items off the
+// head shrank the content height mid-scroll, which read as the list flinging itself
+// to the bottom (worst on the 3-column grids, where dropping a page is not a whole
+// number of rows), and left rows above unreachable. Worst case is the whole catalog
+// in memory — what the pre-Room build did unconditionally — and only for a list you
+// actually scrolled end to end.
 function appendWindow<T>(
   current: T[],
   incoming: T[],
   key: (item: T) => string
 ): T[] {
   const known = new Set(current.map(key));
-  const merged = [...current, ...incoming.filter((item) => !known.has(key(item)))];
-  return merged.length > MAX_WINDOW_ITEMS ? merged.slice(merged.length - MAX_WINDOW_ITEMS) : merged;
+  return [...current, ...incoming.filter((item) => !known.has(key(item)))];
+}
+
+function prependWindow<T>(
+  current: T[],
+  incoming: T[],
+  key: (item: T) => string
+): T[] {
+  const known = new Set(current.map(key));
+  return [...incoming.filter((item) => !known.has(key(item))), ...current];
+}
+
+/**
+ * Dropping back to page 1 under a live scroll offset leaves the list looking at an
+ * offset past the new content end, which lands the user at the bottom of a list they
+ * were reading the middle of. Bumping the revision remounts it (the revision is part
+ * of the list's key) so it comes back at the top instead.
+ */
+function remountIfShorter(
+  current: { sectionJumpRevision: number },
+  previousLength: number,
+  nextLength: number
+): { sectionJumpRevision: number } | Record<string, never> {
+  return previousLength > nextLength
+    ? { sectionJumpRevision: current.sectionJumpRevision + 1 }
+    : {};
 }
 
 export const useLibraryStore = create<LibraryStore>((set, get) => {
@@ -129,17 +170,15 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
     artists: 0,
   };
   let anchorGeneration = 0;
-  let loadingGeneration = 0;
 
-  const beginLoading = () => {
-    const generation = ++loadingGeneration;
-    set({ isPageLoading: true });
-    return generation;
-  };
-
-  const finishLoading = (generation: number) => {
-    if (generation === loadingGeneration) set({ isPageLoading: false });
-  };
+  // Re-entrancy guards, per list and per direction, so a backward refill, a forward
+  // page and a different view's load never block one another — the single shared flag
+  // this replaced serialised all three lists and made outrunning the loader likelier.
+  // A jump needs no guard: it bumps the list's generation, which voids anything already
+  // in flight.
+  type ListKey = 'tracks' | 'albums' | 'artists';
+  const forwardBusy: Record<ListKey, boolean> = { tracks: false, albums: false, artists: false };
+  const backwardBusy: Record<ListKey, boolean> = { tracks: false, albums: false, artists: false };
 
   const onProgress = (progress: ScanProgress) => {
     set({ scanProgress: progress });
@@ -177,16 +216,52 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
       PAGE_SIZE
     );
 
+  // Backward readers only exist for the sorts the A-Z rail is offered for, which are
+  // the only sorts a jump can leave rows above the window in.
+  const readTrackPageBefore = (
+    cursor: string,
+    sort: 'artist' | 'title',
+  ) => AstraLibraryData.getTrackPageBefore<DbTrack>(sort, cursor, PAGE_SIZE);
+
+  const readAlbumPageBefore = (
+    cursor: string,
+    sort: 'artist' | 'name',
+    includeSingles = useSettingsStore.getState().includeSingles,
+  ) => AstraLibraryData.getAlbumPageBefore<Album>(sort, includeSingles, cursor, PAGE_SIZE);
+
+  const readArtistPageBefore = (
+    cursor: string,
+    groupingMode = useSettingsStore.getState().artistGroupingMode,
+    includeCollaborations = get().includeCollabArtists,
+  ) =>
+    AstraLibraryData.getArtistPageBefore<Artist>(
+      'name',
+      groupingMode,
+      includeCollaborations,
+      cursor,
+      PAGE_SIZE
+    );
+
+  const backwardTrackSort = (sort: TrackSort): 'artist' | 'title' | null =>
+    sort === 'artist' || sort === 'title' ? sort : null;
+
+  const backwardAlbumSort = (sort: AlbumSort): 'artist' | 'name' | null =>
+    sort === 'artist' || sort === 'name' ? sort : null;
+
   const resetTracks = async () => {
     const sort = get().trackSort;
     const generation = ++pageGenerations.tracks;
     const page = await readTrackPage(null, sort);
     if (generation !== pageGenerations.tracks || get().trackSort !== sort) return false;
-    set({
-      tracks: page.items ?? [],
+    const items = page.items ?? [];
+    set((current) => ({
+      tracks: items,
       trackNextCursor: page.nextCursor ?? null,
+      trackPrevCursor: null,
       totalTrackCount: page.totalCount ?? 0,
-    });
+      jumpAnchorIndex: 0,
+      ...remountIfShorter(current, current.tracks.length, items.length),
+    }));
     return true;
   };
 
@@ -200,7 +275,14 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
       get().albumSort !== sort ||
       useSettingsStore.getState().includeSingles !== includeSingles
     ) return false;
-    set({ albums: page.items ?? [], albumNextCursor: page.nextCursor ?? null });
+    const items = page.items ?? [];
+    set((current) => ({
+      albums: items,
+      albumNextCursor: page.nextCursor ?? null,
+      albumPrevCursor: null,
+      jumpAnchorIndex: 0,
+      ...remountIfShorter(current, current.albums.length, items.length),
+    }));
     return true;
   };
 
@@ -216,7 +298,14 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
       useSettingsStore.getState().artistGroupingMode !== groupingMode ||
       get().includeCollabArtists !== includeCollaborations
     ) return false;
-    set({ artists: page.items ?? [], artistNextCursor: page.nextCursor ?? null });
+    const items = page.items ?? [];
+    set((current) => ({
+      artists: items,
+      artistNextCursor: page.nextCursor ?? null,
+      artistPrevCursor: null,
+      jumpAnchorIndex: 0,
+      ...remountIfShorter(current, current.artists.length, items.length),
+    }));
     return true;
   };
 
@@ -299,14 +388,17 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
     artistSort: 'name',
     includeCollabArtists: false,
     isScanning: false,
-    isPageLoading: false,
     scanProgress: { ...IDLE_PROGRESS },
     scanError: null,
     trackNextCursor: null,
     albumNextCursor: null,
     artistNextCursor: null,
+    trackPrevCursor: null,
+    albumPrevCursor: null,
+    artistPrevCursor: null,
     sectionAnchors: [],
     sectionJumpRevision: 0,
+    jumpAnchorIndex: 0,
 
     initialize: () => {
       if (!initPromise) {
@@ -455,20 +547,30 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
         useSettingsStore.getState().artistGroupingMode === groupingMode &&
         current.includeCollabArtists === includeCollaborations &&
         activeGeneration === pageGenerations.artists;
+      const collapsesWindow =
+        (!!trackPage && canApplyTrackPage && current.tracks.length > (trackPage.items?.length ?? 0)) ||
+        (!!albumPage && canApplyAlbumPage && current.albums.length > (albumPage.items?.length ?? 0)) ||
+        (!!artistPage && canApplyArtistPage && current.artists.length > (artistPage.items?.length ?? 0));
       set({
         ...(trackPage && canApplyTrackPage ? {
           tracks: trackPage.items ?? [],
           trackNextCursor: trackPage.nextCursor ?? null,
+          trackPrevCursor: null,
           totalTrackCount: trackPage.totalCount ?? current.totalTrackCount,
         } : {}),
         ...(albumPage && canApplyAlbumPage ? {
           albums: albumPage.items ?? [],
           albumNextCursor: albumPage.nextCursor ?? null,
+          albumPrevCursor: null,
         } : {}),
         ...(artistPage && canApplyArtistPage ? {
           artists: artistPage.items ?? [],
           artistNextCursor: artistPage.nextCursor ?? null,
+          artistPrevCursor: null,
         } : {}),
+        ...(collapsesWindow
+          ? { jumpAnchorIndex: 0, sectionJumpRevision: current.sectionJumpRevision + 1 }
+          : {}),
         homeAlbums: homeAlbumPage.items ?? [],
         homeArtists: homeArtistPage.items ?? [],
         folders,
@@ -480,10 +582,10 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
     loadNextTracks: async () => {
       const state = get();
       const cursor = state.trackNextCursor;
-      if (!cursor || state.isPageLoading) return;
+      if (!cursor || forwardBusy.tracks) return;
       const sort = state.trackSort;
       const pageGeneration = pageGenerations.tracks;
-      const loading = beginLoading();
+      forwardBusy.tracks = true;
       try {
         const page = await readTrackPage(cursor, sort);
         if (
@@ -500,18 +602,18 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
           trackNextCursor: page.nextCursor,
         }));
       } finally {
-        finishLoading(loading);
+        forwardBusy.tracks = false;
       }
     },
 
     loadNextAlbums: async () => {
       const state = get();
       const cursor = state.albumNextCursor;
-      if (!cursor || state.isPageLoading) return;
+      if (!cursor || forwardBusy.albums) return;
       const sort = state.albumSort;
       const includeSingles = useSettingsStore.getState().includeSingles;
       const pageGeneration = pageGenerations.albums;
-      const loading = beginLoading();
+      forwardBusy.albums = true;
       try {
         const page = await readAlbumPage(cursor, sort, includeSingles);
         if (
@@ -529,19 +631,19 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
           albumNextCursor: page.nextCursor,
         }));
       } finally {
-        finishLoading(loading);
+        forwardBusy.albums = false;
       }
     },
 
     loadNextArtists: async () => {
       const state = get();
       const cursor = state.artistNextCursor;
-      if (!cursor || state.isPageLoading) return;
+      if (!cursor || forwardBusy.artists) return;
       const sort = state.artistSort;
       const groupingMode = useSettingsStore.getState().artistGroupingMode;
       const includeCollaborations = state.includeCollabArtists;
       const pageGeneration = pageGenerations.artists;
-      const loading = beginLoading();
+      forwardBusy.artists = true;
       try {
         const page = await readArtistPage(cursor, sort, groupingMode, includeCollaborations);
         if (
@@ -560,20 +662,113 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
           artistNextCursor: page.nextCursor,
         }));
       } finally {
-        finishLoading(loading);
+        forwardBusy.artists = false;
       }
     },
 
+    loadPreviousTracks: async () => {
+      const state = get();
+      const cursor = state.trackPrevCursor;
+      const sort = backwardTrackSort(state.trackSort);
+      if (!cursor || !sort || backwardBusy.tracks) return;
+      const pageGeneration = pageGenerations.tracks;
+      backwardBusy.tracks = true;
+      try {
+        const page = await readTrackPageBefore(cursor, sort);
+        if (
+          pageGeneration !== pageGenerations.tracks ||
+          get().trackSort !== sort ||
+          get().trackPrevCursor !== cursor
+        ) return;
+        if (page.error === 'STALE_REVISION') {
+          await resetTracks();
+          return;
+        }
+        set((current) => ({
+          tracks: prependWindow(current.tracks, page.items, (track) => track.path),
+          trackPrevCursor: page.previousCursor,
+        }));
+      } finally {
+        backwardBusy.tracks = false;
+      }
+    },
+
+    loadPreviousAlbums: async () => {
+      const state = get();
+      const cursor = state.albumPrevCursor;
+      const sort = backwardAlbumSort(state.albumSort);
+      if (!cursor || !sort || backwardBusy.albums) return;
+      const includeSingles = useSettingsStore.getState().includeSingles;
+      const pageGeneration = pageGenerations.albums;
+      backwardBusy.albums = true;
+      try {
+        const page = await readAlbumPageBefore(cursor, sort, includeSingles);
+        if (
+          pageGeneration !== pageGenerations.albums ||
+          get().albumSort !== sort ||
+          useSettingsStore.getState().includeSingles !== includeSingles ||
+          get().albumPrevCursor !== cursor
+        ) return;
+        if (page.error === 'STALE_REVISION') {
+          await resetAlbums();
+          return;
+        }
+        set((current) => ({
+          albums: prependWindow(current.albums, page.items, (album) => album.identity_key),
+          albumPrevCursor: page.previousCursor,
+        }));
+      } finally {
+        backwardBusy.albums = false;
+      }
+    },
+
+    loadPreviousArtists: async () => {
+      const state = get();
+      const cursor = state.artistPrevCursor;
+      if (!cursor || state.artistSort !== 'name' || backwardBusy.artists) return;
+      const groupingMode = useSettingsStore.getState().artistGroupingMode;
+      const includeCollaborations = state.includeCollabArtists;
+      const pageGeneration = pageGenerations.artists;
+      backwardBusy.artists = true;
+      try {
+        const page = await readArtistPageBefore(cursor, groupingMode, includeCollaborations);
+        if (
+          pageGeneration !== pageGenerations.artists ||
+          get().artistSort !== 'name' ||
+          useSettingsStore.getState().artistGroupingMode !== groupingMode ||
+          get().includeCollabArtists !== includeCollaborations ||
+          get().artistPrevCursor !== cursor
+        ) return;
+        if (page.error === 'STALE_REVISION') {
+          await resetArtists();
+          return;
+        }
+        set((current) => ({
+          artists: prependWindow(current.artists, page.items, (artist) => artist.artist),
+          artistPrevCursor: page.previousCursor,
+        }));
+      } finally {
+        backwardBusy.artists = false;
+      }
+    },
+
+    // A jump rebuilds the window around the letter: the letter's own page, plus the
+    // page immediately above it. Without that page above, the list would remount with
+    // the letter as row 0 and there would be nothing to scroll back up into — and
+    // `onStartReached` would fire the moment the list mounted at offset 0, cascading
+    // backwards to the head of the catalog.
     jumpToSection: async (cursor) => {
       const state = get();
       const viewMode = state.viewMode;
       if (viewMode !== 'tracks' && viewMode !== 'albums' && viewMode !== 'artists') return false;
       const generation = ++pageGenerations[viewMode];
-      const loading = beginLoading();
-      try {
       if (viewMode === 'tracks') {
         const sort = state.trackSort;
-          const page = await readTrackPage(cursor, sort);
+        const backwardSort = backwardTrackSort(sort);
+        const [page, before] = await Promise.all([
+          readTrackPage(cursor, sort),
+          backwardSort ? readTrackPageBefore(cursor, backwardSort) : Promise.resolve(null),
+        ]);
         if (
           generation !== pageGenerations.tracks ||
           get().viewMode !== viewMode ||
@@ -587,16 +782,25 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
           void resetSectionAnchors();
           return false;
         }
+        const above = before && !before.error ? before : null;
         set((current) => ({
-            tracks: page.items,
+          tracks: [...(above?.items ?? []), ...page.items],
           trackNextCursor: page.nextCursor,
+          trackPrevCursor: above?.previousCursor ?? null,
           totalTrackCount: page.totalCount,
+          jumpAnchorIndex: above?.items.length ?? 0,
           sectionJumpRevision: current.sectionJumpRevision + 1,
         }));
       } else if (viewMode === 'albums') {
         const sort = state.albumSort;
         const includeSingles = useSettingsStore.getState().includeSingles;
-          const page = await readAlbumPage(cursor, sort, includeSingles);
+        const backwardSort = backwardAlbumSort(sort);
+        const [page, before] = await Promise.all([
+          readAlbumPage(cursor, sort, includeSingles),
+          backwardSort
+            ? readAlbumPageBefore(cursor, backwardSort, includeSingles)
+            : Promise.resolve(null),
+        ]);
         if (
           generation !== pageGenerations.albums ||
           get().viewMode !== viewMode ||
@@ -611,21 +815,24 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
           void resetSectionAnchors();
           return false;
         }
+        const above = before && !before.error ? before : null;
         set((current) => ({
-            albums: page.items,
+          albums: [...(above?.items ?? []), ...page.items],
           albumNextCursor: page.nextCursor,
+          albumPrevCursor: above?.previousCursor ?? null,
+          jumpAnchorIndex: above?.items.length ?? 0,
           sectionJumpRevision: current.sectionJumpRevision + 1,
         }));
       } else {
         const sort = state.artistSort;
         const groupingMode = useSettingsStore.getState().artistGroupingMode;
         const includeCollaborations = state.includeCollabArtists;
-          const page = await readArtistPage(
-            cursor,
-            sort,
-            groupingMode,
-            includeCollaborations,
-          );
+        const [page, before] = await Promise.all([
+          readArtistPage(cursor, sort, groupingMode, includeCollaborations),
+          sort === 'name'
+            ? readArtistPageBefore(cursor, groupingMode, includeCollaborations)
+            : Promise.resolve(null),
+        ]);
         if (
           generation !== pageGenerations.artists ||
           get().viewMode !== viewMode ||
@@ -641,16 +848,16 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
           void resetSectionAnchors();
           return false;
         }
+        const above = before && !before.error ? before : null;
         set((current) => ({
-            artists: page.items,
+          artists: [...(above?.items ?? []), ...page.items],
           artistNextCursor: page.nextCursor,
+          artistPrevCursor: above?.previousCursor ?? null,
+          jumpAnchorIndex: above?.items.length ?? 0,
           sectionJumpRevision: current.sectionJumpRevision + 1,
         }));
       }
       return true;
-      } finally {
-        finishLoading(loading);
-      }
     },
 
     recordTrackPlayed: async (path) => {
@@ -678,7 +885,14 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
 
     setTrackSort: (trackSort) => {
       anchorGeneration += 1;
-      set({ trackSort, tracks: [], trackNextCursor: null, sectionAnchors: [] });
+      set({
+        trackSort,
+        tracks: [],
+        trackNextCursor: null,
+        trackPrevCursor: null,
+        jumpAnchorIndex: 0,
+        sectionAnchors: [],
+      });
       persistSetting(TRACK_SORT_KEY, trackSort);
       void resetTracks();
       void resetSectionAnchors();
@@ -686,7 +900,14 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
 
     setAlbumSort: (albumSort) => {
       anchorGeneration += 1;
-      set({ albumSort, albums: [], albumNextCursor: null, sectionAnchors: [] });
+      set({
+        albumSort,
+        albums: [],
+        albumNextCursor: null,
+        albumPrevCursor: null,
+        jumpAnchorIndex: 0,
+        sectionAnchors: [],
+      });
       persistSetting(ALBUM_SORT_KEY, albumSort);
       void resetAlbums();
       void resetSectionAnchors();
@@ -694,7 +915,14 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
 
     setArtistSort: (artistSort) => {
       anchorGeneration += 1;
-      set({ artistSort, artists: [], artistNextCursor: null, sectionAnchors: [] });
+      set({
+        artistSort,
+        artists: [],
+        artistNextCursor: null,
+        artistPrevCursor: null,
+        jumpAnchorIndex: 0,
+        sectionAnchors: [],
+      });
       persistSetting(ARTIST_SORT_KEY, artistSort);
       void resetArtists();
       void resetSectionAnchors();
@@ -706,6 +934,8 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
         includeCollabArtists,
         artists: [],
         artistNextCursor: null,
+        artistPrevCursor: null,
+        jumpAnchorIndex: 0,
         sectionAnchors: [],
       });
       persistSetting(INCLUDE_COLLAB_ARTISTS_KEY, includeCollabArtists ? 'true' : 'false');