test(newos4): guard chat()'s return and tool-turn survival

The regression in 32608bc shipped because nothing exercised chat() itself.
test-chat-return.js runs 7 assertions against the real module: a tool-using
turn must not throw, must return {content, toolTurns}, the orchestrator
projection must keep the answer, a tool-free turn must return too, the lock
must be released after a failed turn, and a second turn must return its own
answer.

Green 7/7 on 8a9333b; against 32608bc it exits 1 (ReferenceError: recent).
Auto-discovered by newos4-maintain (23/23 node tests).

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