fix(ui): a closing dialog's focus restore reaches the dialog left standing above it, and survives a menu

A dialog closing on its own under a standing modal skipped its restore, and the standing modal's
own target was a control inside the closed one: closing it left the focus on <body>. The skipped
target is now handed to the standing dialog, which falls back to it.

Focus on a row of one of the dialog's own menus (the popover engine portals them out of the dialog
root) read as the user walking away, so Back with a menu open left the focus on <body>. A focus in
a popover portal now counts as held, and one still standing is not taken from.

frontend/src/components/ui/Modal.dom.test.tsx

@@ -23,7 +23,7 @@ vi.mock("../../lib/history", () => ({ useBackToClose: () => {} }));
 import Modal from "./Modal";
 import { clearAll, notify } from "../../lib/notifications";
 import { pushLayer, removeLayer, useLayer } from "../../lib/layerStack";
-import { flushSync } from "react-dom";
+import { createPortal, flushSync } from "react-dom";
 
 // Fire a keydown on window (where Modal installs its handler), inside act.
 const press = (key: string, shiftKey = false) =>
@@ -311,6 +311,70 @@ describe("Modal focus trap (offsetParent stubbed 'visible')", () => {
     document.body.removeChild(trigger);
   });
 
+  it("hands its trigger to the dialog left standing above it, which restores it on close", () => {
+    // The standing upper dialog captured ITS restore target while the focus was inside the lower
+    // one — a control that is gone once the lower closes. So the lower skipping its own restore
+    // (above) handed the trigger to no one, and closing the upper left the focus on <body>.
+    // The arrangement keyboard help or the error dialog opened over a dialog actually has.
+    const trigger = document.createElement("button");
+    document.body.appendChild(trigger);
+    trigger.focus();
+    function Siblings() {
+      const [lower, setLower] = useState(true);
+      const [upper, setUpper] = useState(false);
+      return (
+        <>
+          {lower && (
+            <Modal initialFocus="close" title="lower" onClose={() => {}}>
+              <button onClick={() => setUpper(true)}>open upper</button>
+              <button onClick={() => setLower(false)}>close lower</button>
+            </Modal>
+          )}
+          {upper && (
+            <Modal initialFocus="close" title="upper" onClose={() => {}}>
+              <button onClick={() => setUpper(false)}>close upper</button>
+            </Modal>
+          )}
+        </>
+      );
+    }
+    render(<Siblings />);
+    screen.getByText("open upper").focus();
+    act(() => void screen.getByText("open upper").click()); // opened from inside the lower dialog
+    const inUpper = screen.getByText("close upper");
+    inUpper.focus();
+    // The lower closes on its own under the standing upper (`.click()` moves no focus).
+    act(() => void screen.getByText("close lower").click());
+    expect(screen.queryByText("close lower")).toBeNull();
+    expect(document.activeElement).toBe(inUpper);
+    act(() => void inUpper.click());
+    expect(document.activeElement).toBe(trigger);
+    document.body.removeChild(trigger);
+  });
+
+  it("restores the trigger when it closes with the focus in one of its menus", () => {
+    // The popover engine portals a menu out of the dialog's root (it carries no aria-modal), so a
+    // focus on a menu row read as "the user walked away": Back with a menu open inside a dialog
+    // left the focus on <body>. The portal marker is the one `ui/AnchoredPopover` reads too.
+    const trigger = document.createElement("button");
+    document.body.appendChild(trigger);
+    trigger.focus();
+    const portal = document.createElement("div");
+    portal.setAttribute("data-floating-ui-portal", "");
+    document.body.appendChild(portal);
+    const { unmount } = render(
+      <Modal initialFocus="close" title="t" onClose={() => {}}>
+        <Body />
+        {createPortal(<button>menu-row</button>, portal)}
+      </Modal>,
+    );
+    screen.getByText("menu-row").focus();
+    unmount();
+    expect(document.activeElement).toBe(trigger);
+    document.body.removeChild(trigger);
+    document.body.removeChild(portal);
+  });
+
   it("leaves the focus alone when the user moved it out of the dialog themselves", () => {
     // The other half of the same rule, and the branch nothing drove: taking focus back from where
     // the user deliberately put it is the rudest thing a closing dialog can do.