From d73ba9c1962500eb81d53153ddb334e4c94a2a8b Mon Sep 17 00:00:00 2001
From: Meli
 <5aaa86bce934fc3445fc254aab560a40923f10252f92107e665073dede0e04d3@buzz.block.builderlab.xyz>
Date: Sat, 22 Aug 2026 22:44:21 -0400
Subject: [PATCH] test(desktop): start the mid-page coverage burst with a
 gesture
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"fast middle-page scroll settles with continuous mounted coverage" drove
the scroller with bare scrollTop writes right after a prepend. Those are
not reader input, so the virtualizer's bottom intent stayed armed, and
when the prepend's extent resize fired inside the burst window the
settle hook legitimately re-pinned the floor — the coverage read then
measured the wrong viewport (197px hole). The test used to win that race
only because the at-rest settle hold took ~100ms longer to admit the
page; bounding the hold made the race visible (4/10 on WebKit, 5/12 on
Chromium; 0 on the previous commit).

Dispatch one wheel event before the burst, as a real trackpad pass does.
Proven fail-first: with cancel() no longer clearing bottom intent the
test is red 4/4 at 198px; clean product 16/16 Chromium, 12/12 isolated.

Co-authored-by: Meli <5aaa86bce934fc3445fc254aab560a40923f10252f92107e665073dede0e04d3@buzz.block.builderlab.xyz>
Signed-off-by: Meli <5aaa86bce934fc3445fc254aab560a40923f10252f92107e665073dede0e04d3@buzz.block.builderlab.xyz>
---
 desktop/tests/e2e/scroll-history.spec.ts | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/desktop/tests/e2e/scroll-history.spec.ts b/desktop/tests/e2e/scroll-history.spec.ts
index ad460c3fff..45e704308a 100644
--- a/desktop/tests/e2e/scroll-history.spec.ts
+++ b/desktop/tests/e2e/scroll-history.spec.ts
@@ -1338,7 +1338,15 @@ test("fast middle-page scroll settles with continuous mounted coverage", async (
   // Simulate a fast trackpad pass through several middle-page ranges, then
   // stop. The final evaluate emits the last scroll event; all coverage samples
   // after it are passive observations.
+  //
+  // A real trackpad pass starts with a wheel event, and that is what retires
+  // the virtualizer's bottom intent. Programmatic `scrollTop` writes are not
+  // reader input, so without it the prepend's extent resize can legitimately
+  // re-pin the floor mid-burst and the coverage read measures the wrong place.
   await timeline.evaluate((element) => {
+    element.dispatchEvent(
+      new WheelEvent("wheel", { deltaY: -1, bubbles: true }),
+    );
     const maxOffset = element.scrollHeight - element.clientHeight;
     for (const fraction of [0.72, 0.28, 0.64, 0.36, 0.58, 0.44, 0.52]) {
       element.scrollTop = maxOffset * fraction;