List session runs

Use agent__list_session_traces to find runtime traces for a session whose messages are already recorded.

Required input: session_id, using a session_... handle.
Optional inputs: start_time_unix_seconds, end_time_unix_seconds, limit, cursor, sort, and Gateway’s rationale.
Effect: read only.

The transcript must include the runtime’s external_session_id. Without that join key, the tool returns no trace.