saveInflightState() is called from syncInflightAssistantMessage() on every
token. It does localStorage.getItem + JSON.parse + mutate + JSON.stringify +
localStorage.setItem on the full inflight state map. For a 5000-token response
with a 10KB messages array this produces ~36MB of JSON churn per second.
This O(response_length) work per token is the primary source of GC pressure
that causes the renderer to crash (Chrome error codes 4/5). The 13.6-second
RunTask we observed in perf traces is a direct consequence: accumulated rAF
callbacks execute all at once after each multi-second GC pause.
Fix: add _throttledPersist() which writes at most once every 2 seconds during
token streaming. State transitions that matter for crash recovery (tool events,
done, start) still call persistInflightState() directly, so at most 2s of
in-flight progress is lost if the tab crashes mid-stream.
The _persistTimer is cleared on 'done' so the final state is always flushed.
Co-authored with Claude Sonnet 4.6 / Anthropic.
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