avoid reloading the window on queue edits; add clear up next

- moves that straddle the player window, and deletes that are not the
  current track, rebuilt the playlist with setWindow, restarting the
  playing track (a pause). They now reuse rebuildWindow, which re-lays
  the window around the playing item without replacing it.
- deleting the currently playing queued track now removes it from the
  player in place so it advances to the next track without a reload.
- the Up next section header has a clear button that drops the whole
  queued block and resumes the context after the anchor.

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

@@ -851,6 +851,81 @@ class PlaybackControllerTest {
         assertFalse(handle.operations.any { it.startsWith("setWindow") })
     }
 
+    @Test
+    fun clearingTheQueueResumesTheContext() {
+        seedAlbum(3, sourceId = 1)
+        seedSong("x1", "al2")
+
+        controller.playAlbum(1, "al1", 0)
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
+        controller.addToQueue(1, QueueKind.Song, "x1")
+        controller.next()
+        await {
+            controller.state.value.item
+                ?.id == "x1"
+        }
+
+        controller.clearUpNext()
+        await {
+            controller.state.value.item
+                ?.id == "s2"
+        }
+
+        assertTrue(runBlocking { queues.snapshot().upNext }.isEmpty())
+    }
+
+    @Test
+    fun clearingTheQueueWhileOnTheContextKeepsPlaying() {
+        seedAlbum(3, sourceId = 1)
+        seedSong("x1", "al2")
+
+        controller.playAlbum(1, "al1", 0)
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
+        controller.addToQueue(1, QueueKind.Song, "x1")
+        await { runBlocking { controller.upcomingItem()?.id } == "x1" }
+
+        controller.clearUpNext()
+        Thread.sleep(200)
+
+        assertEquals(
+            "s1",
+            controller.state.value.item
+                ?.id,
+        )
+        assertTrue(runBlocking { queues.snapshot().upNext }.isEmpty())
+    }
+
+    @Test
+    fun movingAFarQueuedTrackDoesNotReloadTheWindow() {
+        seedAlbum(3, sourceId = 1)
+        seedAlbumTracks("al2", 60)
+
+        controller.playAlbum(1, "al1", 0)
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
+        controller.addToQueue(1, QueueKind.Album, "al2")
+        await { runBlocking { controller.upcomingItem()?.id } == "al2-b1" }
+
+        handle.operations.clear()
+        runBlocking { controller.move(50, 2) }
+        Thread.sleep(300)
+
+        assertEquals(
+            "s1",
+            controller.state.value.item
+                ?.id,
+        )
+        assertFalse(handle.operations.any { it.startsWith("setWindow") })
+    }
+
     @Test
     fun nextFollowsTheReorderedQueue() {
         seedAlbum(3, sourceId = 1)
@@ -1846,6 +1921,32 @@ class PlaybackControllerTest {
         }
     }
 
+    private fun seedAlbumTracks(
+        albumId: String,
+        count: Int,
+    ) {
+        runBlocking {
+            db.libraryDao().upsertSongs(
+                (1..count).map { track ->
+                    Song(
+                        sourceId = 1,
+                        id = "$albumId-b$track",
+                        albumId = albumId,
+                        artistId = "ar1",
+                        title = "Album $albumId track $track",
+                        album = "Album $albumId",
+                        artist = "Artist",
+                        duration = 100,
+                        track = track.toLong(),
+                        disc = 1,
+                        starred = null,
+                        genre = null,
+                    )
+                },
+            )
+        }
+    }
+
     private fun seedSong(
         id: String,
         albumId: String,