v0.23.1

Performance\n- Reduces sustained CPU and WindowServer load during long streaming responses by throttling full Markdown redraws.\n- Coalesces incoming token updates and prevents overlapping or stale streaming renders.\n- Keeps buffered live tool-call UI intact across transient thread-switch state changes.\n\n## Maintenance\n- Restores the browser test harness's child-process spawn mock for Codex sessions.