Protect editor sessions from unsaved link navigation and unload

packages/block-editor/test/unsaved.test.ts

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+import { expect, test } from "bun:test";
+import { Window } from "happy-dom";
+import { mountUnsavedChangesGuard } from "../src/unsaved.ts";
+
+test("unsaved guard protects unload and ordinary navigation, permits safe links, and cleans up", () => {
+  const window = new Window({ url: "https://email.example.com/builder/one" });
+  const root = window.document.createElement("main");
+  window.document.body.append(root);
+  let dirty = true, allow = false, confirmations = 0;
+  const guard = mountUnsavedChangesGuard(root as unknown as HTMLElement, { hasUnsavedChanges: () => dirty, confirmLeave: () => { confirmations++; return allow; } });
+  const unload = () => { const event = new window.Event("beforeunload", { cancelable: true }); window.dispatchEvent(event); return event.defaultPrevented; };
+  const click = (href: string, target = "") => {
+    const link = window.document.createElement("a"); link.href = href; link.target = target; root.append(link);
+    const event = new window.MouseEvent("click", { bubbles: true, cancelable: true });
+    link.dispatchEvent(event); return event.defaultPrevented;
+  };
+  expect(unload()).toBe(true);
+  expect(click("/builder/two")).toBe(true);
+  expect(click("#content")).toBe(false);
+  expect(click("/builder/two", "_blank")).toBe(false);
+  expect(confirmations).toBe(1);
+  allow = true;
+  expect(click("/builder/two")).toBe(false);
+  dirty = false;
+  expect(unload()).toBe(false);
+  guard.destroy(); guard.destroy(); dirty = true;
+  expect(unload()).toBe(false);
+});