An instrument, not a gate. Seeds a busy channel against the mock bridge and
measures the main-thread cost the headless correctness suite cannot feel.
Two measurements:
- Fast-wheel scroll of the bounded ~200-row window: compositor-cheap
(~0.2ms layout + 1.3ms recalc over a 241-frame, 12k-px burst).
- Prepend re-render cost while scrolled up: ~9-13ms main-thread tick,
attributable to the O(rendered-rows) parent walk (videoReviewContext
rebuild + day-group boundaries + element construction), NOT layout
and NOT leaf-row reconciliation (MessageRow memo bails correctly).
Anchor holds at 0px drift on this path.
Scope limit: measures Chromium reconciliation, not the WKWebView
compositor feel — that remains the real-Tauri macOS pass.
Run: pnpm build && npx playwright test --config=playwright.perf.config.ts
Co-authored-by: Tyler Longwell <tlongwell@squareup.com>
Signed-off-by: Tyler Longwell <tlongwell@squareup.com>
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