mirror of
https://github.com/block/buzz.git
synced 2026-08-18 06:50:31 +02:00
npub17jjz49l9jjmhhk7cac63j8yt9z555n9cw8vk7v5jz4vzw4ppld5qgj57ccandTyler Longwell
7c2587472c
The live trackpad probe (upscroll-trackpad-live.perf.ts) proved the WebKit
compensation defect against real #buzz-bugs but needs staging + a
port-forward + a member nsec, so it can never gate a PR merge. This gate
reproduces the SAME felt-lurch metric under the SAME momentum actuation on
the deterministic mock jitter-corpus bridge — no network, greppable in CI,
on BOTH engines.
Covers both lurch sources (W3 trace, thread):
- CV-realization lurch: jitter-corpus is the heterogeneous 400-row seed
whose estimateRowHeight mismatch T1.1/T1.2 already gate.
- prepend-commit-under-momentum: 400 rows > 300 CHANNEL_HISTORY_LIMIT, so
fetchOlder pages behind an until-cursor. useLoadOlderOnScroll fires off an
IntersectionObserver on a 600px-margin top sentinel — pure geometry,
input-cadence-independent — so momentum triggers it like live.
channelWindowDelayMs=1000 defers the commit so it lands frames later,
under momentum, reproducing the commit race (not an instant same-frame
commit).
Engine fidelity mirrors T1.1/T1.2: overflow-anchor forced 'none' so
Chromium reproduces the shipped WKWebView (no native scroll anchoring);
under playwright.perf-webkit.config.ts this is the real WebKit family.
Three assertions (Eva's thresholds + Quinn's W4 caveat):
- peak felt lurches (|dev|>10px, non-commit) == 0 — the wheel-fight spike.
- smooth frames (|dev|<=1px) >= 99%.
- RMS deviation across the run <= placeholder — the skip-forever guard:
a too-tight staleness skip-bound never fires the correction under
momentum, showing as a run of sub-10px deviations that dodge the peak
gate but sum to main's raw-shift drift. Peak is blind to that shape.
RED at contract 6b9203ca under the WebKit mirror is mandatory and verified:
WebKit 132 lurches / 94.42% smooth / RMS 4.24px; Chromium-with-mirror 131
lurches / 97.87% smooth. Dawn's engine-order-independent W1 fix turns it
green on both engines. Exact lurch and RMS ceilings pinned against Dawn's
first green candidate, same discipline as T1.2.
Co-authored-by: Tyler Longwell <tlongwell@block.xyz>
Signed-off-by: Tyler Longwell <tlongwell@block.xyz>