The expanded "Thinking" block re-ran marked+DOMPurify and re-set
dangerouslySetInnerHTML with the whole growing reasoning text on every
throttled stream delta (~20 Hz) — the O(n²) hole #302 deliberately left
open ("expanded while streaming"). In Safari this saturates the main
thread and freezes the entire tab during long agent runs, including
while the window is minimized (the JS storm keeps running) and on
re-expanding it mid-turn (one huge layout burst).
- streaming-plain-text.tsx (new): chunked plain-text renderer; chunks
split at blank-line boundaries with an append-only stable-prefix
invariant, so per delta only the tail chunk's text node updates —
no marked, no DOMPurify, no innerHTML swaps.
- reasoning-block.tsx: parse markdown only when expanded AND finalized
(one-time); while streaming, render chunked plain text; collapsed
stays parse-free (#302 unchanged).
- message-item.tsx / message-list.tsx: reasoning liveness = part
state:"streaming" AND the turn is live AND the row is the tail —
a part stranded at state:"streaming" (manual Stop during thinking,
or a provider that never emits reasoning-end) finalizes at turn end
and never re-activates when later turns stream.
Verified with the Chrome perf harness: per-delta marked/DOMPurify work
is gone from the hot path; collapsed streaming stays at 0 long tasks
up to 143k tokens even at 4x CPU throttle; finalized expanded blocks
still render parsed markdown. 245 client tests green.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
PR #224 fixed an AI-chat streaming-render regression by moving the React.memo
content signature into the parent: MessageList now snapshots
messageSignature(message) per render and passes it to MessageItem as the
immutable `signature` prop. The existing memo tests only SIMULATED that
parent half by hardcoding `signature={messageSignature(message)}` in their
harness; the real MessageList was never exercised (chat-thread.test.tsx mocks
it out, and there was no message-list.test).
Add message-list.test.tsx that mounts the REAL MessageList (without mocking
MessageItem or messageSignature) and asserts that an in-place mutation of a
reused message object surfaces on re-render. This guards the parent-side
contract: re-caching the signature on message identity (stable across deltas
while parts mutate) would refreeze the row, and this test would fail.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
agent_vscode
claude_code