An agent's design changes over the control channel (engine.execute, engine.batch) are evaluated
ahead on a copy of the session on an `agent` worker, then run on the window thread reusing every
feature computed there (doc::KeptResults, whatever the bounded evaluation cache dropped); the
worker also makes the display meshes of the bodies they end with. Exports run on a copy. While a
change computes, or the agent cursor acts one out, ui.*, inspection and screenshots answer; later
design changes wait their turn. A chip names the command with Stop. A person's edit meanwhile goes
first; a replaced design refuses the request. Preference: Preferences > AI, agent_off_thread, off
by default.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
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