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>
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