Deleting a message in a thread in a tombstoned room makes all "sync" actions hang

### Steps to reproduce

1. Go to a v12 room
2. Press "See old messages"
3. Find a thread in this old v10 room and delete a message in it

### Outcome

#### What did you expect?

The message gets deleted and everything works fine

#### What happened instead?

1. The message doesn't get deleted
2. Pressing on a room in the room list shows the forever spinning circle in an overlay box
* Before leaving the new room, pressing the "See old messages" button shows a page with a spinning circle forever as well
3. I close then open the app
* Everything works fine
* The message I deleted shows up as deleted

### Your phone model

_No response_

### Operating system version

_No response_

### Application version and app store

26.07.1

### Homeserver

_No response_

### Will you send logs?

Yes

### Will you submit a Pull Request?

No

No files, tests, or entry points are named. Reproduce the v12-to-old-v10 room flow in Element X Android: open old messages, delete a threaded message, then trigger room navigation and “See old messages.” Trace the delete and sync handling until the message deletion completes without leaving either action spinning indefinitely.

Written by the indexing model from the issue text.