diff --git a/e2e/tests/us21-tactic-selection.spec.ts b/e2e/tests/us21-tactic-selection.spec.ts
index 131c31b..e48e6d7 100644
--- a/e2e/tests/us21-tactic-selection.spec.ts
+++ b/e2e/tests/us21-tactic-selection.spec.ts
@@ -144,8 +144,8 @@ test.describe('US-21 — tactic selection', () => {
     const dialog = page.getByRole('dialog');
     await expect(dialog).toBeVisible({ timeout: 10_000 });
 
-    // Wait for matrix to load — matrix returns slug IDs, tactic header title contains "discovery"
-    const discoveryHeader = dialog.locator('button[title*="discovery"]').first();
+    // Wait for matrix to load — tactic header title: "Discovery (TA0007) — click to tag this tactic"
+    const discoveryHeader = dialog.locator('button[title*="TA0007"]');
     await expect(discoveryHeader).toBeVisible({ timeout: 10_000 });
     await discoveryHeader.click();
 
@@ -158,16 +158,10 @@ test.describe('US-21 — tactic selection', () => {
     await deleteSimulation(redteamToken, sim.id);
   });
 
-  test.fail('AC-21.6 — Apply from modal includes tactic in result (auto-save)', async ({
+  test('AC-21.6 — Apply from modal includes tactic in result (auto-save)', async ({
     page,
     context,
   }) => {
-    // KNOWN DEFECT: /api/mitre/matrix returns tactic_id as slug ("discovery") but
-    // PATCH /api/simulations/:id expects TA-format ("TA0007"). When a tactic is
-    // selected via the matrix modal and Apply is clicked, the PATCH body contains
-    // tactic_ids: ["discovery"] which the backend rejects with "unknown tactic id".
-    // Fix owner: backend-builder (matrix endpoint must return TA-format tactic IDs)
-    // OR frontend-builder (modal must map slug → TA format before saving).
     const sim = await createSimulation(redteamToken, engagementId, 'AC-21.6 apply tactic');
 
     await seedTokenInStorage(context, redteamToken);
@@ -177,8 +171,8 @@ test.describe('US-21 — tactic selection', () => {
     const dialog = page.getByRole('dialog');
     await expect(dialog).toBeVisible({ timeout: 10_000 });
 
-    // Wait for matrix to load — tactic header title uses slug: "Discovery (discovery)..."
-    const discoveryBtn = dialog.locator('button[title*="discovery"]').first();
+    // Tactic header title: "Discovery (TA0007) — click to tag this tactic"
+    const discoveryBtn = dialog.locator('button[title*="TA0007"]');
     await expect(discoveryBtn).toBeVisible({ timeout: 10_000 });
     await discoveryBtn.click();
 
@@ -189,7 +183,7 @@ test.describe('US-21 — tactic selection', () => {
     // Modal closes
     await expect(dialog).not.toBeVisible({ timeout: 5_000 });
 
-    // This assertion fails because PATCH with slug ID returns 400
+    // Tactic chip appears after auto-save
     await expect(page.getByTestId('mitre-tactic-tag')).toBeVisible({ timeout: 8_000 });
     await expect(page.getByTestId('techniques-tag-list')).toContainText('TA0007');