Exec approval followups were dispatched by sessionKey only. When /new or
/reset rotates the sessionId under that key while an approval is pending,
the resolved followup landed in the new session, surfacing stale approval
output (or 'Exec denied' / continuation text) in a fresh conversation.
Capture the session UUID active when the approval is requested and drop the
followup once the key has been rebound to a different sessionId:
- agent-run followups: carry the expected id on the agent request and drop it
at the gateway as an early preflight, before the handler touches the rebound
session (session-store write, chat/agent run + active-run registration,
dedupe, accepted ack) — not just before model dispatch. Covers elevated and
non-elevated.
- denied / direct fallback followups: resolve the key's current sessionId from
the session store and drop before the channel send.
Fixes#59349.