feat(invariants): require package-owned companions

vitest.e2e.config.ts

@@ -31,6 +31,7 @@ export default defineConfig({
   // through the root tsconfig paths map; the native option cannot do this.
   plugins: [tsconfigPaths({ projects: ['./tsconfig.json'] })],
   test: {
+    setupFiles: ['./scripts/test-invariants.ts'],
     include: ['packages/*/*/tests/**/*.e2e.ts', 'examples/*/tests/**/*.e2e.ts'],
     // Real model calls: generous timeouts, and retries for transient flakes
     // (the shared internal key hits concurrency quotas). No coverage — the