test(e2e): sprint 5 acceptance — US-26 / US-27 / US-28 + adaptations dropdown sprint 2-4

- us26: add AC-26.4 isinstance guard (technique_ids string→400) + AC-26.7 cascade test (DELETE template does not affect instantiated sim)
- us27: add NIT-1 dropdown Escape/click-outside close, NIT-2 empty-engagement dropdown visibility
- 49 sprint 5 tests passing, 206/207 full suite passing (us1 pre-existing isolation issue)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

e2e/tests/us27-instantiate-from-template.spec.ts

@@ -336,4 +336,61 @@ test.describe('US-27 — instantiate from template', () => {
 
     await deleteSimulation(redteamToken, simId);
   });
+
+  // NIT 1 — Dropdown closes on Escape key and on outside click
+  test('NIT-1 — dropdown closes on Escape key press', async ({
+    page,
+    context,
+  }) => {
+    await seedTokenInStorage(context, redteamToken);
+    await page.goto(`/engagements/${engagementId}`);
+
+    await page.getByTestId('new-simulation-dropdown-toggle').click();
+    // Menu is open
+    await expect(page.getByTestId('from-template-btn')).toBeVisible({ timeout: 3_000 });
+
+    // Press Escape
+    await page.keyboard.press('Escape');
+    await expect(page.getByTestId('from-template-btn')).not.toBeVisible({ timeout: 3_000 });
+  });
+
+  test('NIT-1 — dropdown closes when clicking outside', async ({
+    page,
+    context,
+  }) => {
+    await seedTokenInStorage(context, redteamToken);
+    await page.goto(`/engagements/${engagementId}`);
+
+    await page.getByTestId('new-simulation-dropdown-toggle').click();
+    await expect(page.getByTestId('from-template-btn')).toBeVisible({ timeout: 3_000 });
+
+    // Click somewhere outside the dropdown (page heading)
+    await page.getByRole('heading').first().click({ force: true });
+    await expect(page.getByTestId('from-template-btn')).not.toBeVisible({ timeout: 3_000 });
+  });
+
+  // NIT 2 — Empty-engagement SimulationList still shows dropdown
+  test('NIT-2 — engagement with 0 simulations still shows New simulation dropdown', async ({
+    page,
+    context,
+  }) => {
+    // Create a fresh engagement with no simulations
+    const eng = await createEngagement(redteamToken, {
+      name: 'US27 empty eng dropdown',
+      start_date: '2026-01-01',
+    });
+
+    await seedTokenInStorage(context, redteamToken);
+    await page.goto(`/engagements/${eng.id}`);
+
+    // Primary button visible even in empty state
+    await expect(page.getByTestId('new-simulation-btn')).toBeVisible({ timeout: 5_000 });
+
+    // Chevron also visible and functional
+    await page.getByTestId('new-simulation-dropdown-toggle').click();
+    await expect(page.getByTestId('from-template-btn')).toBeVisible({ timeout: 3_000 });
+
+    const tok = await adminToken();
+    await deleteEngagement(tok, eng.id);
+  });
 });