close the test gaps a QA pass found, and de-flake the flaky ones

Verify the Subsonic token hash and salt freshness, and fall back to per-album
songs when the empty-search probe fails with an I/O error instead of
aborting the whole sync.

Add a real-server sync test that mirrors navidrome and gonic into Room and
reads the rows back, plus SyncManager coverage for the success, coalescing
and mid-sync-failure paths.

Cover the sort mapping and delete/ping ViewModels, the download engine's
request flags, the queue helpers, download prefs and migration data
preservation.

Drop the leaked collectors in the ViewModel/queue tests, document the
screenshot tests as render smoke tests, bind a real search term in the
trigram plan test, and assert a positive in-flight invariant alongside the
concurrency timing checks.

app/src/main/kotlin/com/subtracks/data/download/DownloadNotifier.kt

@@ -14,6 +14,7 @@ import com.subtracks.data.repo.DownloadRepository
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.cancel
 import kotlinx.coroutines.launch
 
 /**
@@ -42,6 +43,10 @@ class DownloadNotifier(
         }
     }
 
+    internal fun close() {
+        scope.cancel()
+    }
+
     private fun build(content: DownloadNotification): Notification =
         NotificationCompat
             .Builder(context, CHANNEL_ID)

app/src/main/kotlin/com/subtracks/data/repo/DownloadRepository.kt

@@ -35,6 +35,7 @@ import kotlinx.coroutines.flow.flowOf
 import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
 import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import kotlinx.coroutines.withContext
@@ -78,7 +79,9 @@ class DownloadRepository(
     }
 
     fun close() {
+        val job = scope.coroutineContext[Job]
         scope.cancel()
+        runBlocking { job?.join() }
     }
 
     fun states(): StateFlow<Map<String, SongDownload>> = statesFlow

app/src/main/kotlin/com/subtracks/data/source/subsonic/SubsonicSource.kt

@@ -27,6 +27,7 @@ import kotlinx.coroutines.sync.Semaphore
 import kotlinx.coroutines.sync.withPermit
 import kotlinx.coroutines.withContext
 import org.xml.sax.Attributes
+import java.io.IOException
 
 @OptIn(ExperimentalCoroutinesApi::class)
 class SubsonicSource(
@@ -272,6 +273,8 @@ class SubsonicSource(
                 ) { input -> SubsonicXml.containsEntity(input, "song") }
             } catch (_: SubsonicException) {
                 false
+            } catch (_: IOException) {
+                false
             }
         emptyQuerySearchSupported = supported
         return supported

app/src/main/kotlin/com/subtracks/ui/library/LibraryViewModel.kt

@@ -159,8 +159,8 @@ class LibraryViewModel(
     fun sync() = syncManager.requestSync()
 }
 
-private fun ListQuery.albumSort(): AlbumSort = AlbumSort.entries.firstOrNull { it.name == sort } ?: AlbumSort.Name
+internal fun ListQuery.albumSort(): AlbumSort = AlbumSort.entries.firstOrNull { it.name == sort } ?: AlbumSort.Name
 
-private fun ListQuery.artistSort(): ArtistSort = ArtistSort.entries.firstOrNull { it.name == sort } ?: ArtistSort.Name
+internal fun ListQuery.artistSort(): ArtistSort = ArtistSort.entries.firstOrNull { it.name == sort } ?: ArtistSort.Name
 
-private fun ListQuery.playlistSort(): PlaylistSort = PlaylistSort.entries.firstOrNull { it.name == sort } ?: PlaylistSort.Name
+internal fun ListQuery.playlistSort(): PlaylistSort = PlaylistSort.entries.firstOrNull { it.name == sort } ?: PlaylistSort.Name