fix(deck-picker): do not block the main thread on startup during sync

[criticalAY]

Note

Assisted-by: Claude Opus 4.8 (some diagnosis and a few parts of code)

Purpose / Description

Fixes an ANR when the DeckPicker is recreated while a sync is stuck on an unresponsive server (for example AnkiWeb being down).

Fixes

• Fixes If ankiweb does not respond, the UI does not respond #21305

Approach

See commit

How Has This Been Tested?

Unit test

Learning (optional, can help others)

NA

Checklist

Please, go through these checks before submitting the PR.

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner

[david-allison]

Could you provide reproduction instructions (probably a patch which adds a delay) so we can reproduce it on a physical device.

The startup path has historically been nasty. This initially looks good (and the ViewModel makes things easier), but I'd like to run it through a debugger to confirm.

[criticalAY]

Subject: [PATCH] repro: sync anr
---
Index: AnkiDroid/src/main/java/com/ichi2/anki/Sync.kt
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/AnkiDroid/src/main/java/com/ichi2/anki/Sync.kt b/AnkiDroid/src/main/java/com/ichi2/anki/Sync.kt
--- a/AnkiDroid/src/main/java/com/ichi2/anki/Sync.kt	(revision 25da95364f62624be98404df64afae4d699f134c)
+++ b/AnkiDroid/src/main/java/com/ichi2/anki/Sync.kt	(date 1783413600156)
@@ -159,6 +159,8 @@
             manualCancelButton = R.string.dialog_cancel,
         ) {
             withCol {
+                Timber.w("#21305 repro: holding the collection queue for 60s")
+                Thread.sleep(60_000)
                 syncCollection(auth2, syncMedia = false) // media is synced by SyncMediaWorker
             }
         }
Index: AnkiDroid/src/main/java/com/ichi2/anki/deckpicker/DeckPickerViewModel.kt
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/AnkiDroid/src/main/java/com/ichi2/anki/deckpicker/DeckPickerViewModel.kt b/AnkiDroid/src/main/java/com/ichi2/anki/deckpicker/DeckPickerViewModel.kt
--- a/AnkiDroid/src/main/java/com/ichi2/anki/deckpicker/DeckPickerViewModel.kt	(revision 25da95364f62624be98404df64afae4d699f134c)
+++ b/AnkiDroid/src/main/java/com/ichi2/anki/deckpicker/DeckPickerViewModel.kt	(date 1783413571943)
@@ -522,17 +522,11 @@
         }
 
         Timber.d("handleStartup: Continuing after permission granted")
-        viewModelScope.launch {
-            // opening the collection waits on the collection queue, which a sync stuck on an
-            // unresponsive server can hold for a long time. Waiting on the main thread here
-            // froze the DeckPicker when it was recreated
-            val failure =
-                withContext(Dispatchers.IO) {
-                    InitialActivity.getStartupFailureType(environment::initializeAnkiDroidFolder)
-                }
+        run {
+            val failure = InitialActivity.getStartupFailureType(environment::initializeAnkiDroidFolder)
             if (failure != null) {
                 flowOfStartupResponse.value = StartupResponse.FatalError(failure)
-                return@launch
+                return
             }
 
             // successful startup