fix: subagent questions go to the orchestrator before the user - #23053

Eligibility
This is a contained fix to route ordinary subagent questions through a live orchestrator before surfacing them to the user, with secrets and approvals still surfaced immediately. The wire-format addition is optional and backward-compatible, and targeted tests cover the changed states.

Notes:
No code owners found in target merge base 5a0d159

Agent Credits: 30 credits
Approvability runs at a flat rate of 30 credits whenever the agent is asked for a verdict.