fix(deck-picker) freeze after theme changes

Fixes deadlocking in DeckPicker when changing themes by adding buffers to MutableSharedFlow instances.

The issue occurred because:
1. DeckPicker uses launchCollectionInLifecycleScope which only collects flows when activity is RESUMED
2. During theme changes, the activity is recreated and temporarily not in RESUMED state
3. emit() calls on MutableSharedFlow without buffers would suspend indefinitely when no collectors were active
4. This caused the app to freeze/hang after theme changes

Solution:
- Added extraBufferCapacity = 1 to all MutableSharedFlow instances in DeckPickerViewModel
- This allows emit() calls to succeed even when no collectors are active
- The buffered events will be processed when collectors resume

Fixes 19512

Co-authored-by: raiyyan <[email protected]>

Author: 2 people

AnkiDroid/src/main/java/com/ichi2/anki/deckpicker/DeckPickerViewModel.kt

@@ -105,7 +105,7 @@ class DeckPickerViewModel :
     /**
      * Used if the Deck Due Tree is mutated
      */
-    private val flowOfRefreshDeckList = MutableSharedFlow<Unit>()
+    private val flowOfRefreshDeckList = MutableSharedFlow<Unit>(extraBufferCapacity = 1)
 
     val flowOfDeckList =
         combine(
@@ -130,16 +130,16 @@ class DeckPickerViewModel :
      * @see deleteDeck
      * @see DeckDeletionResult
      */
-    val deckDeletedNotification = MutableSharedFlow<DeckDeletionResult>()
-    val emptyCardsNotification = MutableSharedFlow<EmptyCardsResult>()
-    val flowOfDestination = MutableSharedFlow<Destination>()
-    override val onError = MutableSharedFlow<String>()
+    val deckDeletedNotification = MutableSharedFlow<DeckDeletionResult>(extraBufferCapacity = 1)
+    val emptyCardsNotification = MutableSharedFlow<EmptyCardsResult>(extraBufferCapacity = 1)
+    val flowOfDestination = MutableSharedFlow<Destination>(extraBufferCapacity = 1)
+    override val onError = MutableSharedFlow<String>(extraBufferCapacity = 1)
 
     /**
      * A notification that the study counts have changed
      */
     // TODO: most of the recalculation should be moved inside the ViewModel
-    val flowOfDeckCountsChanged = MutableSharedFlow<Unit>()
+    val flowOfDeckCountsChanged = MutableSharedFlow<Unit>(extraBufferCapacity = 1)
 
     var loadDeckCounts: Job? = null
         private set
@@ -150,9 +150,9 @@ class DeckPickerViewModel :
      */
     private var schedulerUpgradeDialogShownForVersion: Long? = null
 
-    val flowOfPromptUserToUpdateScheduler = MutableSharedFlow<Unit>()
+    val flowOfPromptUserToUpdateScheduler = MutableSharedFlow<Unit>(extraBufferCapacity = 1)
 
-    val flowOfUndoUpdated = MutableSharedFlow<Unit>()
+    val flowOfUndoUpdated = MutableSharedFlow<Unit>(extraBufferCapacity = 1)
 
     val flowOfCollectionHasNoCards = MutableStateFlow(true)
 
@@ -180,7 +180,7 @@ class DeckPickerViewModel :
 
     // HACK: dismiss a legacy progress bar
     // TODO: Replace with better progress handling for first load/corrupt collections
-    val flowOfDecksReloaded = MutableSharedFlow<Unit>()
+    val flowOfDecksReloaded = MutableSharedFlow<Unit>(extraBufferCapacity = 1)
 
     /**
      * Deletes the provided deck, child decks. and all cards inside.