* fix(harness): keep a cancelled batch cancelled when retrying a failed item
retry_item only kept a paused batch as it was, so retrying a failed item
of a cancelled batch reset the batch to queued and the worker claimed and
ran the item. A cancelled batch now rejects the retry (409), re-checked
under the write lock because SQLite ignores FOR UPDATE, and the workspace
no longer offers Retry there.
* docs(changelog): reference #7792 for the cancelled batch retry fix
