ui: validate queue moves against content revisions

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

@@ -586,6 +586,7 @@ class PlaybackController(
         from: Long,
         to: Long,
         resetVersion: Long? = null,
+        expectedContentVersion: Long? = null,
     ): Boolean {
         if (from == to) return false
         val requestedVersion = resetVersion ?: snapshot?.resetVersion ?: return false
@@ -593,6 +594,7 @@ class PlaybackController(
         queueRepository.withMutationLock {
             val snapshot = this@PlaybackController.snapshot ?: return@withMutationLock
             if (snapshot.resetVersion != requestedVersion) return@withMutationLock
+            if (expectedContentVersion != null && snapshot.version != expectedContentVersion) return@withMutationLock
             if (from !in 0 until snapshot.size || to !in 0 until snapshot.size) return@withMutationLock
             val player = player ?: return@withMutationLock
             val current = currentQueuePosition() ?: return@withMutationLock

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

@@ -195,7 +195,7 @@ class QueueViewModel(
             }
         } else {
             val usedIds = updated.mapTo(HashSet()) { it.id }
-            val unresolvedTail = rows.filter { it.id !in usedIds }
+            val unresolvedTail = rows.filter { it.position > end && it.id !in usedIds }
             rows.clear()
             rows.addAll(updated)
             rows.addAll(unresolvedTail)
@@ -302,12 +302,13 @@ class QueueViewModel(
         val resetVersion = rows.firstOrNull { it.position == from }?.resetVersion ?: return rejectMove(edit, onComplete)
         val targetResetVersion = targetResetVersion ?: rows.firstOrNull { it.position == to }?.resetVersion ?: resetVersion
         if (resetVersion != targetResetVersion) return rejectMove(edit, onComplete)
+        val expectedContentVersion = queueRepository.contentVersion()
         reorderPending = true
         viewModelScope.launch {
             try {
                 val applied =
                     mutex.withLock {
-                        val applied = playbackController.move(from, to, resetVersion)
+                        val applied = playbackController.move(from, to, resetVersion, expectedContentVersion)
                         if (!applied) rollbackReorder(edit)
                         reconcileLocked()
                         applied

app/src/test/kotlin/com/subtracks/ui/playback/QueueViewModelTest.kt

@@ -552,6 +552,21 @@ class QueueViewModelTest {
         assertEquals(before.map { it.position }, rowsSnapshot().map { it.position })
     }
 
+    @Test
+    fun reconciliationRemovesADeletedHeadRowFromSparseOfflineRows() {
+        openSparseOfflineQueue()
+        val point = runBlocking { queues.captureResetPoint() }
+        runBlocking {
+            db.libraryDao().deleteSongs(1, listOf("s1"))
+            queues.resetChangedOrigins(setOf(QueueOrigin(QueueKind.Album, 1, "al1")), point)
+        }
+
+        viewModel.reconcile()
+
+        await { rowsSnapshot().map { it.song.song.id } == listOf("s801", "s901") }
+        assertEquals(listOf(800L, 900L), rowsSnapshot().map { it.position })
+    }
+
     @Test
     fun staleRowMoveIsRejectedAfterControllerReconciliation() {
         runBlocking { seedSongs(3) }
@@ -768,6 +783,43 @@ class QueueViewModelTest {
         assertEquals(listOf(0L, 1L, 2L), rowsSnapshot().map { it.position })
     }
 
+    @Test
+    fun moveQueuedBehindRemovalRejectsItsInvalidatedPositions() {
+        runBlocking { seedSongs(4) }
+        controller.playAlbum(1, "al1", 0)
+        await { controller.state.value.position == 0L }
+        viewModel.open()
+        await { viewModel.ready }
+        val before = rowsSnapshot()
+        val paused = pauseQueueMutation()
+        val removalCompletion = CompletableDeferred<Boolean>()
+        val moveCompletion = CompletableDeferred<Boolean>()
+        try {
+            runOnMainSuspending {
+                viewModel.remove(before[0].position, removalCompletion::complete)
+                yield()
+                assertTrue(
+                    viewModel.move(
+                        before[1].position,
+                        before[2].position,
+                        before[1].resetVersion,
+                        moveCompletion::complete,
+                    ),
+                )
+                yield()
+            }
+        } finally {
+            resumeQueueMutation(paused)
+        }
+
+        assertTrue(awaitCompletion(removalCompletion))
+        assertFalse(awaitCompletion(moveCompletion))
+        println("DEBUG reverse rows=${rowsSnapshot().map { it.song.song.id to it.position }} queue=${resolvedQueueIds()}")
+        assertEquals(listOf("s2", "s3", "s4"), resolvedQueueIds())
+        assertEquals(listOf("s2", "s3", "s4"), rowsSnapshot().map { it.song.song.id })
+        assertEquals(listOf(0L, 1L, 2L), rowsSnapshot().map { it.position })
+    }
+
     @Test
     fun moveRejectsRowsFromDifferentResetGenerations() {
         runOnMain {