fix: select next deck after deletion to prevent Default deck appearing in StudyOptionsFragment

[sanjaysargam]

Note

Assisted-by: Claude Opus 4.8

Purpose / Description

On tablets, deleting a deck causes StudyOptionsFragment to display the Default deck, even when other non-Default decks remain.

Fixes

• Fixes Deck deletion causes Default deck to appear in right window when DeckPicker is fragmented #21087

Approach

call sched.deckDueTree() to find the first remaining non-Default deck and decks.select() it, so that when StudyOptionsFragment.opExecuted() subsequently calls withCol { decks.current() }, it reads the correct deck instead of the Default that the backend resets to after removal.

How Has This Been Tested?

Medium Tablet API 35

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

[lukstbit]

Wait for another opinion but I think it would be better if the next selected deck after deleting a deck is one of the deleted deck's siblings or its parent(if it was the only child) so the selection doesn't jump(possible out of screen).

[david-allison]

In addition: the ViewModels to be well-tested, as these will continue to be core functionality after our move to Compose

• Only one opChanges is published
• A few tests about the next deck: child deck, child deck with sibling before/after; child deck with both siblings; parent deck

[david-allison]

I agree with lukstbit: define a 'basic' algorithm to select the next node within the tree/list

[david-allison]

Look into using decks.setCurrent() which returns an opChanges - you will want to test ACTIVE_DECKS is set as expected

Then, consider using two withCol calls, collect the opChanges, combine them, publish as one event

[david-allison]

This comment feels 'Claude':

• Make it less verbose
• State that this explicitly deviates from Anki Desktop
• Mention all of:
  • Unexpected scrolling around the deck list
  • Selecting a 'Default' deck which is not visible in the sidebar (allowing it to be studied)
  • Fragmented View