CHW-4902 ActionAlreadyUndone

action already undone; retrying will not change the state

Default message: action already undone; retrying will not change the state
HTTP status: 409 (client)

Problem. The targeted action has already been rolled back (undone_at is non-null). Cause. The state transition is one-way; retrying with the same id will keep failing the same way. Fix. No action required — the undo has already taken effect. If the original mutation needs to be re-applied, perform a fresh write. HTTP 409.