The hook stamps the payload's tool_use_id, the host logs it and forwards it in a quernstone-turn header, and the server puts it on the span every line of that request is emitted under. The harness's own identifier rather than a fresh one, so the same string also finds the turn in the transcript; never stored, because a repository is public and an operational identifier does not belong in one. Change-Id: I4a915772e85ab94032e5e2c0d277ef5c4aab8c5d