fix(ui): start pointer drags only while the primary button is held (#1071)

On macOS, with an editable element focused and an input method active, WebKit can deliver a tap as pointerup then pointerdown, so drag trackers saw every later pointermove as a held button: one tap plus a pointer move started a phantom drag (file drag label, tab detach, tool window move) and the next tap dropped it. A drag now starts only from a move with the primary button down, a move without it cancels the press, and late button-less moves after a drag started are ignored so the drop is kept. Resizers, dialog drag/resize, pan and the review gutter end instead; the Project view also listens for pointercancel.

Refs #760

Co-authored-by: ntbang0901 <[email protected]>

e2e/projectTree.spec.ts

@@ -1,3 +1,4 @@
+import type { Page } from "@playwright/test";
 import { expect, test } from "./fixtures";
 
 test("keyboard navigation: arrows move, Right/Left expand and collapse, Enter opens", async ({ workbench: page }) => {
@@ -48,3 +49,43 @@ test("Git ignore submenu offers shared and local destinations for files and fold
     await page.keyboard.press("Escape");
   }
 });
+
+// macOS WebKit can deliver a tap's pointerup before its pointerdown, leaving a press with no button held (#760).
+const settle = (page: Page) =>
+  page.evaluate(() => new Promise((done) => requestAnimationFrame(() => requestAnimationFrame(done))));
+
+async function fileRow(page: Page) {
+  // The start-up splash swallows raw mouse presses until it has faded out.
+  await expect(page.locator("#splash")).toHaveCount(0);
+  const file = page.getByRole("tree", { name: "Project" }).getByRole("treeitem", { name: "settings.gradle.kts" });
+  await file.scrollIntoViewIfNeeded();
+  const content = file.locator("[data-project-path]");
+  const box = (await content.boundingBox())!;
+  return {
+    content,
+    x: box.x + 10,
+    y: box.y + box.height / 2,
+    dragLabel: page.locator('body > div[aria-hidden="true"]', { hasText: "settings.gradle.kts" }),
+  };
+}
+
+test("a press without a held button never starts a file drag", async ({ workbench: page }) => {
+  const { content, x, y, dragLabel } = await fileRow(page);
+  await content.evaluate((el) =>
+    el.dispatchEvent(new PointerEvent("pointerdown", { bubbles: true, button: 0, buttons: 0, pointerType: "mouse" })),
+  );
+  await page.mouse.move(x, y);
+  await page.mouse.move(x + 60, y + 30, { steps: 5 });
+  await settle(page);
+  await expect(dragLabel).toHaveCount(0);
+});
+
+test("a real mouse drag still shows the drag label until release", async ({ workbench: page }) => {
+  const { x, y, dragLabel } = await fileRow(page);
+  await page.mouse.move(x, y);
+  await page.mouse.down();
+  await page.mouse.move(x + 60, y + 30, { steps: 5 });
+  await expect(dragLabel).toHaveCount(1);
+  await page.mouse.up();
+  await expect(dragLabel).toHaveCount(0);
+});