fix drag drop target, serialize queue edits, guard empty ranges

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

@@ -437,6 +437,49 @@ class PlaybackControllerTest {
         )
     }
 
+    @Test
+    fun movingTracksFarFromThePlayingOneDoesNotReloadTheWindow() {
+        seedAlbum(100, sourceId = 1)
+
+        controller.playAlbum(1, "al1", 50)
+        await {
+            controller.state.value.item
+                ?.id == "s51"
+        }
+        handle.operations.clear()
+
+        runBlocking { controller.move(80, 90) }
+
+        assertEquals(
+            "s51",
+            controller.state.value.item
+                ?.id,
+        )
+        assertEquals(50L, controller.state.value.position)
+        assertFalse(handle.operations.any { it.startsWith("setWindow") })
+    }
+
+    @Test
+    fun movingATrackAcrossTheWindowKeepsPlaying() {
+        seedAlbum(100, sourceId = 1)
+
+        controller.playAlbum(1, "al1", 50)
+        await {
+            controller.state.value.item
+                ?.id == "s51"
+        }
+        handle.operations.clear()
+
+        runBlocking { controller.move(10, 90) }
+
+        assertEquals(
+            "s51",
+            controller.state.value.item
+                ?.id,
+        )
+        assertFalse(handle.operations.any { it.startsWith("setWindow") })
+    }
+
     @Test
     fun undoRestoresARemovedTrack() {
         seedAlbum(5, sourceId = 1)

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

@@ -82,6 +82,22 @@ class QueueViewModelTest {
         assertEquals((40L..199L).toList(), viewModel.rows.map { it.position })
     }
 
+    @Test
+    fun openingAtTheEndLoadsASingleRowAndExtendsOlder() {
+        runBlocking { seedSongs(200) }
+        controller.playSongs(1, 199)
+        await { controller.state.value.position == 199L }
+
+        viewModel.open()
+        await { viewModel.ready }
+
+        assertEquals(listOf(199L), viewModel.rows.map { it.position })
+
+        viewModel.loadOlder()
+        await { viewModel.rows.firstOrNull()?.position == 139L }
+        assertEquals((139L..199L).toList(), viewModel.rows.map { it.position })
+    }
+
     @Test
     fun reorderingMovesTheRowLocally() {
         runBlocking { seedSongs(200) }