test(17-03): add FAB↔BottomTabBar overlap regression guard to layout.spec.ts

- New test: "New Event FAB does not overlap BottomTabBar (A — phone only)"
- Skips on desktop profile; runs iphone + pixel (the profiles that exposed D-01)
- Asserts fabBox.y + fabBox.height <= navBox.y (FAB bottom ≤ bar top)
- Confirms Task 1 fix resolves the seed defect — passes green on both profiles

apps/pwa/e2e/layout.spec.ts

@@ -199,6 +199,40 @@ test.describe('Rule 2 — No horizontal overflow', () => {
   });
 });
 
+// ── D-01 Regression Guard: FAB does not overlap BottomTabBar (Workstream A) ──
+//
+// Permanent overlap assertion for the seed defect: New Event FAB was landing on the
+// Admin tab at 390×844, clipping the color-legend chips behind the BottomTabBar.
+// Fixed by calc(var(--bottom-chrome-h) + var(--space-6)) in CalendarShell.tsx.
+// Runs on iphone + pixel (the profiles that exposed the issue); skipped on desktop.
+
+test.describe('D-01 regression guard — FAB does not overlap BottomTabBar', () => {
+  test('New Event FAB does not overlap BottomTabBar (A — phone only)', async ({
+    page,
+  }, testInfo) => {
+    test.skip(testInfo.project.name === 'desktop', 'Phone-only assertion');
+
+    await page.goto('/calendar');
+
+    const fab = page.getByRole('button', { name: 'New Event' });
+    const nav = page.getByRole('navigation', { name: 'Main navigation' });
+
+    await expect(fab).toBeVisible();
+    await expect(nav).toBeVisible();
+
+    const fabBox = await fab.boundingBox();
+    const navBox = await nav.boundingBox();
+
+    expect(fabBox, 'New Event FAB bounding box must not be null').not.toBeNull();
+    expect(navBox, 'BottomTabBar bounding box must not be null').not.toBeNull();
+
+    expect(
+      fabBox!.y + fabBox!.height,
+      `FAB bottom edge (${fabBox!.y + fabBox!.height}) must be ≤ BottomTabBar top edge (${navBox!.y}) — no overlap`,
+    ).toBeLessThanOrEqual(navBox!.y);
+  });
+});
+
 // ── Harness self-validation — injected-defect proofs (TEST-01 acceptance bar) ──
 //
 // Each test is a PASSING test that proves the assertion would have failed under a