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test(studio): inject a 45 ms stall per timeline scroll step to prove the gate fails it #4848

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test(studio): inject a 45 ms stall per timeline scroll step to prove the gate fails it #4848

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c90286d
fix(studio): the timeline viewport gate judges p95 over every measure…
miguel-heygen Oct 1, 2026
c2388b2
test(studio): inject a 45 ms stall per timeline scroll step to prove …
miguel-heygen Oct 1, 2026
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1 change: 1 addition & 0 deletions packages/studio/src/player/components/useTimelineScrollViewport.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,7 @@ export function useTimelineScrollViewport(
const scrollingRef = useRef(false);

const syncScrollViewport = useCallback((el: HTMLDivElement, isScrolling = false) => {
if (isScrolling) for (const end = performance.now() + 45; performance.now() < end; );
// Row virtualization is the only consumer of the per-frame scroll snapshot.
// With the flag off, publishing it re-rendered every mounted clip on every
// scroll frame and bought nothing, so the scroll path stops here and
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2 changes: 1 addition & 1 deletion packages/studio/src/player/lib/timelineViewportBudgets.test.ts
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Expand Up @@ -23,7 +23,7 @@ describe("timeline viewport budgets", () => {
constrainedLongTaskLimitMs: 300,
posterCoverageRatio: 0.9,
supportedFixtureFallbackRatio: 0.02,
scrollSamplesPerRun: 21,
scrollSamplesPerRun: 63,
warmupRuns: 3,
measuredRuns: 5,
requiredPassingRuns: 4,
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2 changes: 1 addition & 1 deletion packages/studio/src/player/lib/timelineViewportBudgets.ts
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Expand Up @@ -99,7 +99,7 @@ export const TIMELINE_VIEWPORT_BUDGETS: Readonly<TimelineViewportBudgets> = Obje
richPreviewP95Ms: 750,
constrainedRichPreviewP95Ms: 1_200,
supportedFixtureFallbackRatio: 0.02,
scrollSamplesPerRun: 21,
scrollSamplesPerRun: 63,
warmupRuns: 3,
measuredRuns: 5,
requiredPassingRuns: 4,
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26 changes: 13 additions & 13 deletions packages/studio/tests/e2e/timeline-virtualization.mjs
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Expand Up @@ -90,6 +90,8 @@ async function collectRun(page, injectedLongTaskMs = 0) {
interactionP95Ms: percentileInPage(interactions, 0.95),
frameIntervalP95Ms: percentileInPage(frameIntervals, 0.95),
scrollSampleCount: interactions.length,
interactions,
frameIntervals,
longestTaskMs: Math.max(0, ...longTasks),
scrollWidth: scroller.scrollWidth,
scrollHeight: scroller.scrollHeight,
Expand Down Expand Up @@ -319,19 +321,21 @@ try {
// so a skipped budget never reads as a passed one.
const domBudgetsApply = ROW_VIRTUALIZATION === "on";
for (const run of runs) {
run.responsivenessPassed =
run.interactionP95Ms <= interactionLimitMs &&
run.frameIntervalP95Ms <= frameIntervalLimitMs &&
run.longestTaskMs <= longTaskLimitMs;
run.longTaskPassed = run.longestTaskMs <= longTaskLimitMs;
run.timelineMounted = run.diagnostics.timelineRoots === 1;
run.domSizePassed = domBudgetsApply
? run.diagnostics.mountedRows <= budgets.maxMountedRows &&
run.diagnostics.mountedClipRoots <= budgets.maxMountedClipRoots &&
run.diagnostics.maxMountedClipRootsInOneRow <= budgets.maxMountedClipRootsPerRow &&
run.diagnostics.mountedTimelineDescendants <= budgets.maxMountedTimelineDescendants
: null;
run.passed = run.responsivenessPassed && run.timelineMounted && run.domSizePassed !== false;
run.passed = run.longTaskPassed && run.timelineMounted && run.domSizePassed !== false;
}
// Pooled over every measured step: one run's p95 is only its 4th-worst step, so a brief runner stall failed it.
const interactionP95Ms = percentile(runs.flatMap((run) => run.interactions), 0.95);
const frameIntervalP95Ms = percentile(runs.flatMap((run) => run.frameIntervals), 0.95);
const responsivenessPassed =
interactionP95Ms <= interactionLimitMs && frameIntervalP95Ms <= frameIntervalLimitMs;

await page.evaluate(() => window.__studioTest.resetTimelinePerformanceFixture());
await page.waitForFunction(
Expand Down Expand Up @@ -386,14 +390,9 @@ try {
directScrollGate,
runs,
aggregate: {
interactionP95Ms: percentile(
runs.map((run) => run.interactionP95Ms),
0.95,
),
frameIntervalP95Ms: percentile(
runs.map((run) => run.frameIntervalP95Ms),
0.95,
),
interactionP95Ms,
frameIntervalP95Ms,
responsivenessPassed,
passingRuns,
baselineHeapBytes,
returnedHeapBytes,
Expand All @@ -403,6 +402,7 @@ try {
console.log(JSON.stringify(evidence, null, 2));
exitCode =
directScrollGate.decision === "approved" &&
responsivenessPassed &&
passingRuns >= budgets.requiredPassingRuns &&
memoryReturned
? 0
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