test: add jsdom Popover API shim

vitest.setup.jsdom.ts

@@ -61,3 +61,48 @@ if (typeof PointerEvent === 'undefined') {
 // jsdom lacks pointer capture
 HTMLElement.prototype.setPointerCapture = vi.fn();
 HTMLElement.prototype.releasePointerCapture = vi.fn();
+
+// jsdom lacks the Popover API. Minimal shim: methods toggle an internal flag,
+// dispatch a `toggle` event ({ oldState, newState }), and make
+// matches(':popover-open') reflect the flag so components can sync state.
+if (typeof HTMLElement.prototype.showPopover !== 'function') {
+    const openFlag = new WeakSet<HTMLElement>();
+
+    const fireToggle = (el: HTMLElement, oldState: string, newState: string) => {
+        const event = new Event('toggle') as Event & { oldState: string; newState: string };
+        event.oldState = oldState;
+        event.newState = newState;
+        el.dispatchEvent(event);
+    };
+
+    HTMLElement.prototype.showPopover = function showPopover(this: HTMLElement) {
+        if (openFlag.has(this)) {
+            return;
+        }
+        openFlag.add(this);
+        fireToggle(this, 'closed', 'open');
+    };
+    HTMLElement.prototype.hidePopover = function hidePopover(this: HTMLElement) {
+        if (!openFlag.has(this)) {
+            return;
+        }
+        openFlag.delete(this);
+        fireToggle(this, 'open', 'closed');
+    };
+    HTMLElement.prototype.togglePopover = function togglePopover(this: HTMLElement) {
+        if (openFlag.has(this)) {
+            this.hidePopover();
+            return !openFlag.has(this);
+        }
+        this.showPopover();
+        return openFlag.has(this);
+    };
+
+    const originalMatches = Element.prototype.matches;
+    Element.prototype.matches = function matches(this: Element, selector: string): boolean {
+        if (selector === ':popover-open') {
+            return this instanceof HTMLElement && openFlag.has(this);
+        }
+        return originalMatches.call(this, selector);
+    } as typeof Element.prototype.matches;
+}