Drives the reverse path end to end over REST loopback: a worker is delegated
a task it cannot finish without asking, calls bridge_ask mid-turn, and the
primary answers on the surfaced turnId so the worker resumes the SAME turn.
Two blocking sends, no polling. Verified live: worker asked in ~9s, resumed
and replied CHOSEN=BLUE via clean bridge_reply after the primary answered.
Subscription-safe by construction (REST face only; never sets ANTHROPIC_BASE_URL).
Dai Ha