Prevent whole-window scroll bounce

src/shared/styles/globals.css

@@ -68,6 +68,8 @@
     background: var(--workspace);
     font-synthesis: none;
     -webkit-font-smoothing: antialiased;
+    /* Keep wheel/trackpad gestures from rubber-banding the whole app. */
+    overscroll-behavior: none;
   }
   * {
     box-sizing: border-box;

tests/browser/layout.spec.mjs

@@ -71,6 +71,48 @@ async function shellFits(page, width) {
   }
 }
 
+test("page overscroll is disabled while message history still scrolls", async ({
+  page,
+  app,
+}) => {
+  await open(page, app);
+  // Headless wheel input does not reproduce macOS trackpad rubber-banding.
+  // Check the viewport policy as well as real panel scrolling and shell bounds.
+  await expect(page.locator("html")).toHaveCSS("overscroll-behavior", "none");
+  const shell = page.locator(".shell-background");
+  const bounds = await box(shell);
+  const history = page.getByRole("region", { name: "Channel message history" });
+  await settle(page);
+  const initialOffset = await history.evaluate((el) => el.scrollTop);
+  await history.hover();
+  await page.mouse.wheel(0, -300);
+  await expect
+    .poll(() => history.evaluate((el) => el.scrollTop))
+    .toBeLessThan(initialOffset - 100);
+  await settle(page);
+  expect(await box(shell)).toEqual(bounds);
+
+  // Projects has no overflowing content: gestures must leave the shell in place.
+  await page
+    .getByRole("navigation", { name: "Pages", exact: true })
+    .getByRole("button", { name: "Projects", exact: true })
+    .click();
+  await page.getByRole("heading", { name: "Projects", exact: true }).hover();
+  for (const [x, y] of [
+    [0, -600],
+    [0, 600],
+    [-600, 0],
+    [600, 0],
+  ]) {
+    await page.mouse.wheel(x, y);
+    await page.evaluate(() => new Promise(requestAnimationFrame));
+    expect(await box(shell)).toEqual(bounds);
+    expect(await page.evaluate(() => [window.scrollX, window.scrollY])).toEqual(
+      [0, 0],
+    );
+  }
+});
+
 test("bento surfaces, centered tabs, real link panel and compact community navigation", async ({
   page,
   app,

tests/browser/typeahead.spec.mjs

@@ -534,7 +534,8 @@ test("current custom catalog drives typeahead and signed tags across community r
   await expect(input).toHaveValue(":party-parrot ");
   await input.press("ControlOrMeta+z");
   await expect(input).toHaveValue(":party-parrot: ");
-  await input.press("End");
+  // macOS End scrolls the document; use its caret shortcut when overscroll is off.
+  await input.press(process.platform === "darwin" ? "Meta+ArrowRight" : "End");
   await input.pressSequentially("hello");
   await expect(input).toHaveValue(":party-parrot: hello");
   await input.press("Enter");