queue view: stop reloading on edits, fix drag boundaries

- deleting a track no longer bumps the layout version, so the view does
  not reload and jump to the current track; the ViewModel already
  updates its rows.
- layout changes (re-anchor, enqueue, consume) now reconcile positions in
  place instead of calling open(), which cleared the rows and scrolled
  back to the cursor.
- section headers are separate list items and reordering maps by key, so
  the header no longer rides along with a dragged row (top flicker).
- disable the reorderable auto-scroll (scrollThreshold = 0). The library
  scrolls past the section boundary with no valid target, then abandons
  the scroll on release; without auto-scroll a drag stays put and drops
  in the last reachable slot.
- keep the current track when moving a queued track before it (eager
  dispatcher regression test).

app/src/main/kotlin/com/subtracks/playback/PlaybackController.kt

@@ -344,7 +344,6 @@ class PlaybackController(
                     RemovedUndo(entries, cursor, target, position, removed, snapshot.shuffleOrder, upNext, snapshot.upNextAnchor)
                 }
             if (snapshot.upNextSize > 0L || updated.upNextSize > 0L) {
-                layoutVersion++
                 queueRepository.setCursor(target)
                 loadWindow(target, autoplay = playing, startPositionMs = if (position == current) 0 else player.currentPositionMs)
                 return@withLock

app/src/main/kotlin/com/subtracks/ui/playback/QueueScreen.kt

@@ -133,6 +133,30 @@ class QueueViewModel(
         }
     }
 
+    fun reconcile() {
+        viewModelScope.launch {
+            mutex.withLock {
+                if (!ready) return@withLock
+                val snapshot = queueRepository.snapshot()
+                if (snapshot.size == 0L) {
+                    rows.clear()
+                    return@withLock
+                }
+                val start = (rows.firstOrNull()?.position ?: 0L).coerceIn(0, snapshot.size - 1)
+                val end = (start + rows.size.coerceAtLeast(QUEUE_CHUNK) - 1).coerceAtMost(snapshot.size - 1)
+                val loaded = queueRepository.range(snapshot, start, end)
+                val reused = reusedIds()
+                val updated = loaded.map { rowFor(it, reused) }
+                if (updated.size == rows.size) {
+                    updated.forEachIndexed { index, row -> if (rows[index] != row) rows[index] = row }
+                } else {
+                    rows.clear()
+                    rows.addAll(updated)
+                }
+            }
+        }
+    }
+
     fun loadOlder() {
         val top = rows.firstOrNull()?.position ?: return
         if (top <= 0L) return
@@ -265,7 +289,8 @@ fun QueueRoute(
     LaunchedEffect(queueContext) {
         sourceTitle.value = controller.sourceTitle(queueContext)?.takeIf { it.isNotBlank() } ?: fallbackTitle
     }
-    LaunchedEffect(playback.shuffle, playback.layout, open) { if (open) viewModel.open() }
+    LaunchedEffect(playback.shuffle, open) { if (open) viewModel.open() }
+    LaunchedEffect(playback.layout) { if (open) viewModel.reconcile() }
     QueueScreen(
         rows = viewModel.rows,
         ready = viewModel.ready,
@@ -283,7 +308,6 @@ fun QueueRoute(
         onLoadOlder = viewModel::loadOlder,
         onLoadNewer = viewModel::loadNewer,
         onUndo = viewModel::undo,
-        onRefresh = viewModel::open,
         modifier = modifier,
     )
 }
@@ -308,7 +332,6 @@ fun QueueScreen(
     generation: Int = 0,
     shuffle: Boolean = false,
     contextTitle: String? = null,
-    onRefresh: () -> Unit = {},
 ) {
     val listState = rememberLazyListState()
     val fill = rememberViewportFill(listState)
@@ -318,25 +341,25 @@ fun QueueScreen(
     var dragFrom by remember { mutableStateOf<Long?>(null) }
 
     val upNextReorder =
-        rememberReorderableLazyListState(listState) { from, to ->
+        rememberReorderableLazyListState(listState, scrollThreshold = 0.dp) { from, to ->
-            onReorder(from.index, to.index)
+            onReorder(rows.rowIndexOf(from.key), rows.rowIndexOf(to.key))
         }
     val contextReorder =
-        rememberReorderableLazyListState(listState) { from, to ->
+        rememberReorderableLazyListState(listState, scrollThreshold = 0.dp) { from, to ->
-            onReorder(from.index, to.index)
+            onReorder(rows.rowIndexOf(from.key), rows.rowIndexOf(to.key))
         }
 
     LaunchedEffect(listState, ready, generation) {
         if (!ready) return@LaunchedEffect
-        if (initialIndex > 0) listState.scrollToItem(initialIndex)
+        if (initialIndex > 0) listState.scrollToItem(rows.lazyIndexOf(initialIndex))
         snapshotFlow {
             val info = listState.layoutInfo
-            val firstVisible = info.visibleItemsInfo.firstOrNull()?.index ?: -1
+            val first = info.visibleItemsInfo.firstOrNull { it.key is Long }?.let { rows.rowIndexOf(it.key) } ?: -1
-            val lastVisible = info.visibleItemsInfo.lastOrNull()?.index ?: -1
+            val last = info.visibleItemsInfo.lastOrNull { it.key is Long }?.let { rows.rowIndexOf(it.key) } ?: -1
-            firstVisible to lastVisible
+            first to last
-        }.collect { (firstVisible, lastVisible) ->
+        }.collect { (first, last) ->
-            if (firstVisible in 0..LOAD_THRESHOLD) onLoadOlder()
+            if (first in 0..LOAD_THRESHOLD) onLoadOlder()
-            if (lastVisible >= 0 && lastVisible >= rows.size - 1 - LOAD_THRESHOLD) onLoadNewer()
+            if (last >= 0 && last >= rows.size - 1 - LOAD_THRESHOLD) onLoadNewer()
         }
     }
 
@@ -377,12 +400,14 @@ fun QueueScreen(
                     modifier = Modifier.padding(padding).fillMaxSize(),
                     contentPadding = PaddingValues(bottom = 16.dp),
                 ) {
-                    items(count = rows.size, key = { rows[it].id }) { index ->
+                    rows.forEachIndexed { index, row ->
-                        val row = rows[index]
                         if (index == 0 || rows[index - 1].upNext != row.upNext) {
+                            item(key = "header-$index") {
                                 QueueSectionHeader(if (row.upNext) "Up next" else contextTitle ?: "Next up")
                             }
+                        }
                         val enabled = row.upNext || !shuffle
+                        item(key = row.id) {
                             ReorderableItem(
                                 state = if (row.upNext) upNextReorder else contextReorder,
                                 key = row.id,
@@ -412,18 +437,16 @@ fun QueueScreen(
                                                     val id = dragId
                                                     val from = dragFrom
                                                     if (id != null && from != null) {
-                                                    val index = rows.indexOfFirst { it.id == id }
+                                                        val draggedIndex = rows.indexOfFirst { it.id == id }
-                                                    val to = if (index < 0) from else dropTarget(rows, index, from)
+                                                        val to =
-                                                    val left = rows.getOrNull(index - 1)?.upNext
+                                                            if (draggedIndex < 0) {
-                                                    val right = rows.getOrNull(index + 1)?.upNext
+                                                                from
-                                                    val sameSection =
+                                                            } else {
-                                                        (left == null || left == row.upNext) &&
+                                                                dropTarget(rows, draggedIndex, from)
-                                                            (right == null || right == row.upNext)
+                                                            }
-                                                    if (to != from && sameSection) {
+                                                        if (to != from) {
                                                             onMove(from, to)
                                                             showUndo("Queue reordered")
-                                                    } else if (to != from) {
-                                                        onRefresh()
                                                         }
                                                     }
                                                     dragId = null
@@ -439,7 +462,8 @@ fun QueueScreen(
                                 )
                             }
                         }
-                    item { Spacer(Modifier.height(fill)) }
+                    }
+                    item(key = "fill") { Spacer(Modifier.height(fill)) }
                 }
             }
         }
@@ -456,6 +480,20 @@ private fun QueueSectionHeader(label: String) {
     )
 }
 
+private fun List<QueueRow>.rowIndexOf(key: Any?): Int {
+    val id = key as? Long ?: return -1
+    return indexOfFirst { it.id == id }
+}
+
+private fun List<QueueRow>.lazyIndexOf(rowIndex: Int): Int {
+    if (rowIndex !in indices) return 0
+    var headers = 0
+    for (i in 0..rowIndex) {
+        if (i == 0 || this[i - 1].upNext != this[i].upNext) headers++
+    }
+    return rowIndex + headers
+}
+
 internal fun dropTarget(
     rows: List<QueueRow>,
     index: Int,

app/src/test/kotlin/com/subtracks/playback/PlaybackControllerTest.kt

@@ -690,6 +690,49 @@ class PlaybackControllerTest {
         eager.close()
     }
 
+    @Test
+    fun movingAQueuedTrackBeforeTheCurrentDoesNotConsumeIt() {
+        seedAlbum(3, sourceId = 1)
+        seedSong("q1", "al2")
+        seedSong("q2", "al2")
+        seedSong("q3", "al2")
+        val eagerHandle = FakePlayerHandle()
+        val inline =
+            object : kotlinx.coroutines.CoroutineDispatcher() {
+                override fun dispatch(
+                    context: kotlin.coroutines.CoroutineContext,
+                    block: Runnable,
+                ) = block.run()
+            }
+        val eager = PlaybackController(sources, queues, FakePlayerConnection(eagerHandle), dispatcher = inline)
+
+        eager.playAlbum(1, "al1", 0)
+        await {
+            eager.state.value.item
+                ?.id == "s1"
+        }
+        eager.addToQueue(1, QueueKind.Song, "q1")
+        eager.addToQueue(1, QueueKind.Song, "q2")
+        eager.addToQueue(1, QueueKind.Song, "q3")
+        await { runBlocking { eager.upcomingItem()?.id } == "q1" }
+        eager.playAt(2)
+        await {
+            eager.state.value.item
+                ?.id == "q2"
+        }
+
+        runBlocking { eager.move(3, 2) }
+        Thread.sleep(300)
+
+        assertEquals(
+            "q2",
+            eager.state.value.item
+                ?.id,
+        )
+        assertEquals(3, runBlocking { queues.snapshot().upNext.size })
+        eager.close()
+    }
+
     @Test
     fun nextFollowsTheReorderedQueue() {
         seedAlbum(3, sourceId = 1)