docs: state what the save timeout and a racing delete actually guarantee (#51, #37)

The tracker comment said 'never a stalled job'; each transition can wait up to the timeout.
The delete refusal is judged at the moment of the attempt. Found by the PR #58 review.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

DECISIONS.md

@@ -1556,7 +1556,9 @@ deferred. The scope cut — chat first, no rich analysis, no video — is what k
   mechanism), confirm-then-delete on the recording's page. A recording that is **queued or
   transcribing is refused (409) until it ends**, because the worker would otherwise write to a
   row that is gone; a job whose service was lost stays undeletable until the next start's sweep
-  marks it failed. The home list now links to `/uploads` when uploads are mounted.
+  marks it failed. The refusal reflects the row's state when the delete was attempted: a
+  recording that finishes in the same instant still gets a 409 once, and a retry deletes it.
+  The home list now links to `/uploads` when uploads are mounted.
 
 **Reversibility.** Additive: one table (down-migration drops it), one adapter, one upload
 surface, one image change. Removing the upload route removes the feature; `transcripts`, `videos`