New subfolder collapsing enabled by default without memory

Checklist

• I have used the search function to see if someone else has already submitted the same bug report.
• I will describe the problem with as much detail as possible.

App

Thunderbird for Android

App version

12.1

Where did you get the app from?

F-Droid

Android version

16

Device model

Pixel 8 Pro

Steps to reproduce

Have a mailbox with subfolders

Behavior

My mailbox is set up like this:

Bulk
Bulk/Receipts
Bulk/House
Family
Family/Child 1
Family/Child 2
...

Prior to the changes in I think #9045, these were not a collapsing hierarchy, and I could choose which subfolders were displayed, which was useful because I basically /always/ want to see Family/Child 1 and Family/Child 2 (and in fact Family/ is an empty subfolder).

Currently, all folders are collapsed by default, and even when I uncollapse them, they will occasionally revert to all-collapsed if I leave the app for too long. I don't need the old behavior, but if the collapsed/uncollapsed state were persisted, I could leave things collapsed or uncollapsed as desired.

Start by reproducing the folder collapsing behavior in Thunderbird for Android 12.1 with a mailbox containing nested subfolders, then inspect the changes associated with #9045. Done means the chosen collapsed or expanded state remains after leaving the app and returning later.