On long agent runs (dozens of tool calls) the desktop app froze at 100% CPU with
no user interaction: useChat updated state on every streamed token, and
MessageItem/ReasoningBlock re-parsed the whole transcript's markdown (the marked
pipeline + DOMPurify) on every delta. Per-turn work grew quadratically and
saturated the main thread; the SSE stream drove it, so it hung "on its own".
- chat-thread: pass experimental_throttle (50ms) to useChat so the streamed
messages state re-renders at most ~20 Hz instead of once per token.
- message-item: memoize MessageItem on a cheap per-message content signature
(the streaming tail still re-renders as it grows; finalized rows are skipped),
and render each text part via a memoized MarkdownPart so finalized parts are
not re-parsed. The signature includes usage.reasoningTokens so the
authoritative "Thinking - N tokens" count still snaps in at finish-step.
- reasoning-block: memoize the markdown render (useMemo on the text) and wrap the
component in React.memo.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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