The autosave I had just added appended a new message on every debounce, so a
few minutes of typing would have left the Drafts folder holding a dozen copies
of the same unfinished mail. Caught before deploying.
The composer now returns the stored UID and sends it back as replace_uid on
the next save; the use case expunges the superseded draft, but only after the
replacement has committed, so a failure leaves the older draft in place rather
than losing both. Expunge is a soft delete matching the expunged_at column the
schema already uses, and it locates the message by mailbox as well as UID so a
caller cannot delete someone else's mail by guessing a number.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
