test(web): preserve threshold edits across controlled disclosure toggles

Threshold table tests replace the disclosure with a mock, so they cannot protect the controlled collapse/reopen behaviour used by snapshot controls. Exercise the real disclosure with reactive parent state and verify accessibility attributes and retained input identity/value without claiming browser focus or installed-release recovery evidence.

Change-source: pulse-maintainer

frontend-modern/src/components/Alerts/Thresholds/sections/__tests__/CollapsibleSection.test.tsx

@@ -1,4 +1,5 @@
 import { afterEach, describe, expect, it, vi } from 'vitest';
+import { createSignal } from 'solid-js';
 import { cleanup, fireEvent, render, screen } from '@solidjs/testing-library';
 import { CollapsibleSection, SectionActionButton, NestedGroupHeader } from '../CollapsibleSection';
 import {
@@ -173,6 +174,47 @@ describe('CollapsibleSection', () => {
     expect(button).toHaveAttribute('aria-expanded', 'false');
   });
 
+  it('preserves an edited threshold across controlled collapse and reopen', () => {
+    const [collapsed, setCollapsed] = createSignal(true);
+    render(() => (
+      <CollapsibleSection
+        id="snapshots"
+        title="Snapshot Age"
+        collapsed={collapsed()}
+        onToggle={setCollapsed}
+      >
+        <label>
+          Warning days
+          <input type="number" value="7" />
+        </label>
+      </CollapsibleSection>
+    ));
+
+    const disclosure = screen.getByRole('button', { name: 'Snapshot Age' });
+    const panel = document.getElementById(disclosure.getAttribute('aria-controls')!);
+    expect(panel).toHaveAttribute('inert');
+    expect(panel).toHaveAttribute('aria-hidden', 'true');
+
+    fireEvent.click(disclosure);
+    expect(disclosure).toHaveAttribute('aria-expanded', 'true');
+    expect(panel).not.toHaveAttribute('inert');
+    expect(panel).not.toHaveAttribute('aria-hidden');
+    const input = screen.getByRole('spinbutton', { name: 'Warning days' });
+    fireEvent.input(input, { target: { value: '14' } });
+
+    fireEvent.click(disclosure);
+    expect(disclosure).toHaveAttribute('aria-expanded', 'false');
+    expect(panel).toHaveAttribute('inert');
+    expect(panel).toHaveAttribute('aria-hidden', 'true');
+
+    fireEvent.click(disclosure);
+    expect(disclosure).toHaveAttribute('aria-expanded', 'true');
+    expect(panel).not.toHaveAttribute('inert');
+    expect(panel).not.toHaveAttribute('aria-hidden');
+    expect(screen.getByRole('spinbutton', { name: 'Warning days' })).toBe(input);
+    expect(input).toHaveValue(14);
+  });
+
   it('shows "Disabled" badge when isGloballyDisabled is true', () => {
     render(() => (
       <CollapsibleSection id="test" title="Title" isGloballyDisabled={true}>