diff --git a/client/src/components/WindowManager/WindowManagerWindow.test.ts b/client/src/components/WindowManager/WindowManagerWindow.test.ts
new file mode 100644
index 00000000000..6aff6ba8d58
--- /dev/null
+++ b/client/src/components/WindowManager/WindowManagerWindow.test.ts
@@ -0,0 +1,149 @@
+import { createTestingPinia } from "@pinia/testing";
+import { getLocalVue } from "@tests/vitest/helpers";
+import { mount } from "@vue/test-utils";
+import { setActivePinia } from "pinia";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import { useWindowManagerStore } from "@/stores/windowManagerStore";
+
+import WindowManagerWindow from "./WindowManagerWindow.vue";
+
+const localVue = getLocalVue();
+
+// happy-dom does not implement pointer capture, so stub it. Capturing the
+// pointer is what keeps drag/resize alive when the cursor crosses an iframe
+// (the center frame or the window's own body), so we assert on these calls.
+const setPointerCapture = vi.fn();
+
+function pointerEvent(type: string, options: PointerEventInit = {}) {
+    return new PointerEvent(type, { bubbles: true, cancelable: true, button: 0, pointerId: 7, ...options });
+}
+
+function mountWindow() {
+    const pinia = createTestingPinia({ createSpy: vi.fn, stubActions: false });
+    setActivePinia(pinia);
+    const store = useWindowManagerStore();
+    store.add({ title: "GalaxyAI", url: "/galaxyai", x: 50, y: 60, width: 400, height: 300 });
+    const win = store.windows[0]!;
+    const wrapper = mount(WindowManagerWindow as object, {
+        localVue,
+        pinia,
+        propsData: { window: win },
+    });
+    return { wrapper, win };
+}
+
+describe("WindowManagerWindow", () => {
+    beforeEach(() => {
+        (HTMLElement.prototype as any).setPointerCapture = setPointerCapture;
+    });
+
+    afterEach(() => {
+        vi.clearAllMocks();
+        delete (HTMLElement.prototype as any).setPointerCapture;
+    });
+
+    it("resizes with the pointer and captures it on the handle", () => {
+        const { wrapper, win } = mountWindow();
+        const handle = wrapper.find(".window-manager-resize-handle");
+
+        handle.element.dispatchEvent(pointerEvent("pointerdown", { clientX: 450, clientY: 360 }));
+        expect(setPointerCapture).toHaveBeenCalledWith(7);
+
+        document.dispatchEvent(pointerEvent("pointermove", { clientX: 550, clientY: 410 }));
+        expect(win.width).toBe(500);
+        expect(win.height).toBe(350);
+
+        document.dispatchEvent(pointerEvent("pointerup", { clientX: 550, clientY: 410 }));
+        document.dispatchEvent(pointerEvent("pointermove", { clientX: 650, clientY: 460 }));
+        expect(win.width).toBe(500);
+        expect(win.height).toBe(350);
+    });
+
+    it("drags with the pointer and captures it on the header", () => {
+        const { wrapper, win } = mountWindow();
+        const header = wrapper.find(".window-manager-window-header");
+
+        header.element.dispatchEvent(pointerEvent("pointerdown", { clientX: 200, clientY: 80 }));
+        expect(setPointerCapture).toHaveBeenCalledWith(7);
+
+        document.dispatchEvent(pointerEvent("pointermove", { clientX: 230, clientY: 120 }));
+        expect(win.x).toBe(80);
+        expect(win.y).toBe(100);
+
+        document.dispatchEvent(pointerEvent("pointerup", { clientX: 230, clientY: 120 }));
+        document.dispatchEvent(pointerEvent("pointermove", { clientX: 300, clientY: 200 }));
+        expect(win.x).toBe(80);
+        expect(win.y).toBe(100);
+    });
+
+    it("stops resizing when the pointer is cancelled", () => {
+        const { wrapper, win } = mountWindow();
+        const handle = wrapper.find(".window-manager-resize-handle");
+
+        handle.element.dispatchEvent(pointerEvent("pointerdown", { clientX: 450, clientY: 360 }));
+        document.dispatchEvent(pointerEvent("pointermove", { clientX: 550, clientY: 410 }));
+        expect(win.width).toBe(500);
+
+        document.dispatchEvent(pointerEvent("pointercancel", { clientX: 550, clientY: 410 }));
+        document.dispatchEvent(pointerEvent("pointermove", { clientX: 650, clientY: 460 }));
+        expect(win.width).toBe(500);
+        expect(win.height).toBe(350);
+    });
+
+    it("does not start a drag from the window controls", () => {
+        const { wrapper, win } = mountWindow();
+        const controls = wrapper.find(".window-manager-window-controls");
+
+        controls.element.dispatchEvent(pointerEvent("pointerdown", { clientX: 420, clientY: 70 }));
+        document.dispatchEvent(pointerEvent("pointermove", { clientX: 500, clientY: 200 }));
+        expect(win.x).toBe(50);
+        expect(win.y).toBe(60);
+    });
+
+    it("ignores a second pointer while dragging", () => {
+        const { wrapper, win } = mountWindow();
+        const header = wrapper.find(".window-manager-window-header");
+
+        header.element.dispatchEvent(pointerEvent("pointerdown", { clientX: 200, clientY: 80 }));
+        header.element.dispatchEvent(pointerEvent("pointerdown", { pointerId: 9, clientX: 300, clientY: 200 }));
+
+        document.dispatchEvent(pointerEvent("pointermove", { pointerId: 9, clientX: 400, clientY: 300 }));
+        expect(win.x).toBe(50);
+        expect(win.y).toBe(60);
+
+        document.dispatchEvent(pointerEvent("pointermove", { clientX: 230, clientY: 120 }));
+        expect(win.x).toBe(80);
+        expect(win.y).toBe(100);
+
+        document.dispatchEvent(pointerEvent("pointerup", { clientX: 230, clientY: 120 }));
+    });
+
+    it("does not steal focus when clicking the controls of an unfocused window", () => {
+        const pinia = createTestingPinia({ createSpy: vi.fn, stubActions: false });
+        setActivePinia(pinia);
+        const store = useWindowManagerStore();
+        store.add({ title: "First", url: "/a", x: 50, y: 60, width: 400, height: 300 });
+        store.add({ title: "Second", url: "/b" });
+        const first = store.windows[0]!;
+        const second = store.windows[1]!;
+        const wrapper = mount(WindowManagerWindow as object, {
+            localVue,
+            pinia,
+            propsData: { window: first },
+        });
+        expect(store.focusedId).toBe(second.id);
+
+        // a real click delivers pointerdown plus a compatibility mousedown;
+        // neither may bubble to the root focus handler from the controls
+        const controls = wrapper.find(".window-manager-window-controls");
+        controls.element.dispatchEvent(pointerEvent("pointerdown", { clientX: 420, clientY: 70 }));
+        controls.element.dispatchEvent(new MouseEvent("mousedown", { bubbles: true, cancelable: true, button: 0 }));
+        expect(store.focusedId).toBe(second.id);
+
+        const header = wrapper.find(".window-manager-window-header");
+        header.element.dispatchEvent(pointerEvent("pointerdown", { clientX: 200, clientY: 80 }));
+        expect(store.focusedId).toBe(first.id);
+        document.dispatchEvent(pointerEvent("pointerup", { clientX: 200, clientY: 80 }));
+    });
+});