test(frontend): exercise the container update-alerts card controls

The card from f8e8135a3 had model-level coverage only; nothing rendered
the toggle or delay input. Pin the interaction contract: toggle off
writes -1 and hides the delay input, toggle on restores the previous
positive delay (factory 24 when enabling from a persisted off state),
and delay edits clamp to a positive whole hour so 0 (backend 'unset',
silently reset to 24) can never be produced from the UI.

frontend-modern/src/components/Alerts/__tests__/ThresholdsTableDockerUpdateAlertsSection.test.tsx

@@ -0,0 +1,95 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { cleanup, fireEvent, render, screen } from '@solidjs/testing-library';
+import { createSignal } from 'solid-js';
+
+import { ThresholdsTableDockerUpdateAlertsSection } from '@/components/Alerts/ThresholdsTableDockerUpdateAlertsSection';
+import type { ThresholdsTableSectionProps } from '@/features/alerts/thresholds/thresholdsTableSectionProps';
+import { getAlertThresholdsDockerUpdatePresentation } from '@/utils/alertThresholdsPresentation';
+import { FACTORY_DOCKER_DEFAULTS } from '@/utils/alertThresholdDefaults';
+
+type DockerDefaultsShape = typeof FACTORY_DOCKER_DEFAULTS;
+
+// The card owns the only UI lever for updateAlertDelayHours (#1545): the
+// toggle must write -1 (off) — never 0, which the backend resets to 24 —
+// and restore the previous positive delay when re-enabled.
+function renderSection(initialDelayHours: number) {
+  const [dockerDefaults, setDockerDefaultsSignal] = createSignal<DockerDefaultsShape>({
+    ...FACTORY_DOCKER_DEFAULTS,
+    updateAlertDelayHours: initialDelayHours,
+  });
+  const setHasUnsavedChanges = vi.fn();
+  const setDockerDefaults = vi.fn(
+    (update: (prev: DockerDefaultsShape) => DockerDefaultsShape) => {
+      setDockerDefaultsSignal((prev) => update(prev));
+    },
+  );
+
+  const props = {
+    state: {
+      dockerUpdatePresentation: getAlertThresholdsDockerUpdatePresentation(),
+      dockerUpdateDelayInputId: 'docker-update-alert-delay',
+    },
+    tableProps: {
+      get dockerDefaults() {
+        return dockerDefaults();
+      },
+      setDockerDefaults,
+      setHasUnsavedChanges,
+    },
+  } as unknown as ThresholdsTableSectionProps;
+
+  const utils = render(() => <ThresholdsTableDockerUpdateAlertsSection {...props} />);
+  return { ...utils, dockerDefaults, setHasUnsavedChanges };
+}
+
+afterEach(cleanup);
+
+describe('ThresholdsTableDockerUpdateAlertsSection', () => {
+  it('renders the delay input while enabled and hides it when off', () => {
+    const { dockerDefaults } = renderSection(24);
+
+    const input = screen.getByLabelText('Delay (hours)') as HTMLInputElement;
+    expect(input.value).toBe('24');
+
+    fireEvent.click(screen.getByRole('button', { pressed: true }));
+
+    expect(dockerDefaults().updateAlertDelayHours).toBe(-1);
+    expect(screen.queryByLabelText('Delay (hours)')).toBeNull();
+  });
+
+  it('saves -1 on toggle off and restores the prior delay on toggle on', () => {
+    const { dockerDefaults, setHasUnsavedChanges } = renderSection(48);
+
+    const toggle = screen.getByRole('button', { pressed: true });
+    fireEvent.click(toggle);
+    expect(dockerDefaults().updateAlertDelayHours).toBe(-1);
+
+    fireEvent.click(toggle);
+    expect(dockerDefaults().updateAlertDelayHours).toBe(48);
+    expect(setHasUnsavedChanges).toHaveBeenCalledWith(true);
+  });
+
+  it('falls back to the factory delay when enabling from a persisted off state', () => {
+    const { dockerDefaults } = renderSection(-1);
+
+    expect(screen.queryByLabelText('Delay (hours)')).toBeNull();
+
+    fireEvent.click(screen.getByRole('button', { pressed: false }));
+    expect(dockerDefaults().updateAlertDelayHours).toBe(
+      FACTORY_DOCKER_DEFAULTS.updateAlertDelayHours,
+    );
+  });
+
+  it('clamps delay input edits to a positive whole number of hours', () => {
+    const { dockerDefaults } = renderSection(24);
+
+    const input = screen.getByLabelText('Delay (hours)') as HTMLInputElement;
+    fireEvent.input(input, { target: { value: '0' } });
+    // 0 would read as "unset" server-side and silently become 24; the input
+    // clamps to the minimum positive delay instead.
+    expect(dockerDefaults().updateAlertDelayHours).toBe(1);
+
+    fireEvent.input(input, { target: { value: '72' } });
+    expect(dockerDefaults().updateAlertDelayHours).toBe(72);
+  });
+});