🤖 perf: let React Compiler compile MessageRenderer and AssistantMessage

[ThomasK33]

Summary

MessageRenderer and AssistantMessage now compile under React Compiler and leave the guard baseline. Both render once per transcript row.

Implementation

• MessageRenderer reassigned its destructured message prop (message = useStreamingMessageDelta(...)), which the compiler can't lower. The prop is now destructured as messageProp, and the streamed value is a new const message.
• AssistantMessage's fork handler had ?? inside try/catch; it now uses runWithCatch with the same body and error handler.

Validation

• Guard: 13/18 hot components compile (5 known skipped).
• src/browser/features/Messages unit tests (incl. MessageRenderer.test.tsx) and tests/ui/chat/forkFromResponse.test.ts pass.

Measurements

Electron perf e2e (tests/e2e/scenarios/perf.*.spec.ts, XUM_PROFILE_REACT=1), local, serial, 3 runs each, medians. Baseline is main at 349657d; "after" is the top of this stack (#4429), because the layers were measured together. React time is the summed actualDuration of the profiled subtrees.

Scenario	Profiled subtree	main	stack top
Open chat with a 1000-file review	chat-pane.transcript	388 ms	292 ms
Open chat with a 1000-file review	chat-pane.input	76 ms	61 ms
Open chat with a 1000-file review	all profiled	530 ms	424 ms
Open workspace, large history	chat-pane.transcript	331 ms	295 ms
Open workspace, large history	chat-pane.input	52 ms	46 ms
Open workspace, medium history	chat-pane.transcript	206 ms	191 ms

Commit counts are unchanged; the gain is less work per commit. Typing in a large chat and the review hunk specs show no change beyond noise. ChatInput alone, measured before #4418 landed: New Workspace typing went from 165 CreationControls renders per run to 2.

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Generated with xum • Model: anthropic:claude-opus-5-5 • Thinking: high • Cost: $4.05

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-24T15:30:20.306797Z	a973197	New commits
🔒 Security Review	✅ Completed 2026-09-24T15:32:14.827498Z	a973197	New commits

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