Sealed in the vault, not in SharedPreferences — and that is the whole
point. A draft is plaintext the person has not decided to send, very
often the most sensitive text in the app because it is the thing they
are still weighing. SharedPreferences writes readable XML that survives
into backups; the vault seals it under the conversation's own key with
the record name bound into the AAD, and forgetEverything takes it on
sign-out. There is a test that asserts the bytes on disk do not contain
the text, because the wrong implementation would pass every other test
here.
Keyed by the same threadFor* ids the transcript uses, so a group called
"7", the contact who is user 7, and the address "7" are three
different drafts.
Every write to the composer state goes through one setDraft: send clears
it by assigning directly in three places, and any one of those that
forgot to clear the stored copy would bring the message back next time
as a draft of something already sent.
Closes#47 on iOS side; Android half of the same feature
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
