F1: StreamingPlainText/PlainChunk render untrusted model reasoning as a React
text node (escaped), NOT via innerHTML — the load-bearing security property. The
existing tests asserted via textContent, which strips tags, so they couldn't
tell an escaped literal from injected DOM: a future switch to
dangerouslySetInnerHTML would reintroduce XSS with zero failing tests. Add a test
feeding an <img onerror> + <b> payload and asserting querySelector("img"/"b") is
null AND the raw markup survives in textContent — non-vacuous (fails if the
string were parsed as HTML).
F2: the .reasoningText CSS note still described the removed <Text> pre-wrap
fallback and pointed at reasoning-block.tsx (both stale), while PlainChunk's JSDoc
points back to this note — a broken mutual reference. Update the note to point at
PlainChunk / streaming-plain-text.tsx, where pre-wrap is now applied.
No production rendering logic changed. vitest: 8 passed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Mounts the real ChatThread against a synthetic AI SDK v6 UI-message SSE
stream (multi-step reasoning + getPage tool calls + markdown answer;
5k/20k/50k-token presets, 15/5 ms chunk cadence) with long-task, FPS
and mount-time instrumentation. Two scenarios: mount a persisted
transcript (open-chat cost) and stream a live turn through the real
useChat pipeline via a window.fetch patch scoped to /api/ai-chat/stream.
Served only by the vite dev server at /perf/ai-chat-perf.html; the
production build keeps its single index.html entry, so none of this
ships. Also ignore local trace dumps under .claude/perf-traces/.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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>
claude code agent 227
agent_vscode