Test Case 1a: Simple page (no parallel routes)

Interception route with just a page.tsx, no parallel routes at all.

Test Case 1b: Has page.tsx

Interception route has page.tsx at root level. No children slot exists.

Test Case 2: No parallel routes

No @parallel routes exist, so no implicit layout created.

Test Case 3: Has both @sidebar AND page.tsx

Has @sidebar parallel route BUT page.tsx fills the children slot.

Test Case 4a: Has @sidebar but NO page.tsx (implicit layout)

Has @sidebar (creates implicit layout) but NO page.tsx.

✓ Auto-uses null default (no explicit files needed)

Test Case 4b: Has explicit layout.tsx but NO parallel routes

Has explicit layout.tsx with children slot, but NO parallel routes like @sidebar.

? Should it 404 or 200? This determines if we need to check for explicit layouts!