next.js

291aefd9 - Fix 404 responses for interception routes with missing children slots (#85779)

Fix 404 responses for interception routes with missing children slots (#85779) ### What? Introduces a null-rendering default component for interception routes to prevent 404 responses when children slots are missing. ### Why? When rendering interception routes like `(.)[id]`, there's a segment mismatch where the interception route lacks a children slot that the base `[id]` route has. **The Bug:** Previously, the framework injected a 404 page into the missing default slot for the children route. On platforms like Vercel, this caused full 404 RSC responses because the HTTP status code has semantic meaning for route behavior when using cache components. This resulted in the "unknown segment value fallback page" issue. **Impact:** - RSC requests for interception routes would return 404 status codes - Platform routing behavior was incorrectly triggered by these 404 responses - Only affects pages rendering with cache components ### How? - Created new `default-null.tsx` builtin component that renders `null` - Updated Rust code (`app_structure.rs`) to detect interception routes and use the null default - Updated webpack loader (`next-app-loader/index.ts`) to check `isInterceptionRouteAppPath()` and inject the null default - Removed test-specific default component that was working around this bug - The old `page.tsx` is still used during client navigation, so there's no visible change to users This ensures minimal RSC payload changes and prevents 404 status codes while maintaining existing client-side behavior. NAR-483