test(app): make chat outline transit timing deterministic

packages/app/e2e/support/helpers/chat-outline.ts

@@ -77,6 +77,9 @@ export async function expectNoChatOutlinePreview(page: Page): Promise<void> {
 
 export async function expectNoChatOutlinePreviewWhileCrossingToSidebar(page: Page): Promise<void> {
   const railBox = await requireBoundingBox(chatOutlineRail(page));
+  const clockStart = Date.now();
+  await page.clock.install({ time: clockStart });
+  await page.clock.pauseAt(clockStart + 60_000);
   await page.mouse.move(railBox.x + railBox.width + 2, railBox.y + railBox.height / 2);
   await page.evaluate(() => {
     document.body.dataset.chatOutlinePreviewObserved = String(
@@ -91,19 +94,19 @@ export async function expectNoChatOutlinePreviewWhileCrossingToSidebar(page: Pag
     Object.assign(window, { __chatOutlinePreviewObserver: observer });
   });
 
-  for (let step = 0; step <= 10; step += 1) {
+  // Keep the transit slower than the activation delay at every point while making the whole
+  // crossing longer than it. Horizontal motion must keep postponing activation until leave
+  // cancels the final pending timer.
+  const transitSteps = 6;
+  for (let step = 0; step < transitSteps; step += 1) {
     await page.mouse.move(
-      railBox.x + railBox.width - 1 - (step * railBox.width) / 10,
+      railBox.x + railBox.width - 1 - (step * railBox.width) / transitSteps,
       railBox.y + railBox.height / 2,
     );
-    await page.evaluate(
+    await page.clock.runFor(100);
-      () =>
-        new Promise<void>((resolve) => {
-          requestAnimationFrame(() => requestAnimationFrame(() => resolve()));
-        }),
-    );
   }
   await page.mouse.move(railBox.x - 2, railBox.y + railBox.height / 2);
+  await page.clock.runFor(200);
 
   const previewAppeared = await page.evaluate(() => {
     const observer = Reflect.get(window, "__chatOutlinePreviewObserver") as