Timing issue with large drafts

[kesselb]

Steps to reproduce

1. Open Inbox
2. Draft a new message
3. Embed an image
4. Save as draft
5. Change to Drafts folder
6. Open the draft
7. Make some changes
8. Close the composer
9. Open the draft again

Since drafts are immutable, updating a draft deletes the old message and creates a new one. If the user is quick or the sync is slow, the draft being deleted can still appear in the list after closing the composer.

Reopening that envelope/draft leads to a state where A) further edits fails or B) an Nextcloud error page is used as message content (see screencast).

Expected behavior

• Envelope should be removed on saving draft / composer closed: fix(composer): drop envelope from store when saving a draft #12322
• The composer should handle error response from the backend properly: fix(composer): handle missing message body gracefully  #12323

Additional info

Screencast.From.2026-01-27.19-23-36.mp4