An operational run failure with the last confirmed execution state.

reason retains the underlying error category; partial has the same fields as a successful run result, with output: nil and a failed/cancelled status. Incomplete model output is in partial.pending_response, never executable conversation history. Preserving progress does not make replay idempotent.

The partial model is a live runtime value and may contain credentials. Use the message/snapshot codecs rather than exporting this struct as JSON.