This holds the remote error code returned during this specific FSM run of the endpoint's sync, mirroring the endpoint-level remote invocation error code. Because each sync attempt is tracked as its own FSM run, this per-run error code lets an admin see the exact remote-side error that occurred on a specific historical attempt, even after later attempts have succeeded and changed the parent object's live status. A historical FSM run record showing a non-zero error code here documents that a specific past sync attempt for this endpoint failed with a particular peer-side error, useful for pattern-spotting recurring failures.