Identifies where the action happens: which provider, which object, and an optional concurrency token.
| Field | Type | Description |
|---|---|---|
system * | string | Lowercase provider id (e.g., `gmail`, `ms_graph`, `google_calendar`). |
external_id | string | Opaque provider-assigned id. Required for update/delete/reply; omit for create-in-default-container. |
etag | string | Optional optimistic-concurrency token. Executors check before mutating. |