Nothing had ever refreshed a token: the fixture plants no refresh token and there was no endpoint to spend one at, so the write every command makes was reachable only through unit tests of the pieces. It is the operation both the per-identity file and the per-identity lock exist for -- the lock is held across the token request inside it -- and it is the path of the incident this tree documents, where a refresh presenting the wrong `client_id` is answered `invalid_grant` and the session is deleted over it. The test logs in, expires the access token, and asserts a neighbouring identity's file is untouched and the grant survives. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Change-Id: I2f5bd7ff9fedaf5f8495d23a3e1134761672d072