Codex flagged (C) a test-sufficiency gap: the completion-notice fake had
`agent.id === session.header.id`, so the notice test could not distinguish the
code matching on the registry KEY (agentId) from matching on the session TOKEN
(session.header.id). The production code deliberately matches on
`session.header.id` because a config agent has `agentId !== sessionId` — but a
same-value fake passes either way (the "hits the line but not the scenario"
trap).
Give the registered fake a distinct agentId (`agent-<sessionId>`). Verified the
notice test now FAILS if the match is regressed to `a.id` and passes on
`a.session.header.id` — so it actually pins the discriminating behavior.
Tianyi Cui
be6cf4510b