_session_auth_user_id read auth_identity off the transport slot at build time, but a second window replaces that slot with a FanoutTransport that has no identity, and branch and eager-resume builds run before the record exists, so those agents got user_id None. The record now carries auth_user_id from the creating transport, builds that run before the record pass it to _make_agent explicitly, and the compute host turn frame carries it too. A different login attaching to an existing session is logged once with both ids and the creator's id is kept.
Erosika