Drives handleChatRequest with the real practice agent + faux engine:
pose persists its ack and owes no continuation; a commit arrives as the
'Committed answer:' user message and the conclude turn continues to the
reveal; a nudge carries the 'Thinking trace' label and never concludes;
Esc's silent marker deactivates at once and the next input rides the
synthesized dismissed-conclude pair (shared CONCLUDE_ACK_TEXT).
