perf(router): skip paginator checks for plain JSON

Guard paginator duck typing behind the distinguishing data field so ordinary object responses serialize directly. A live CPU profile of the warm static JSON route reduced formatResult self-time from 12.7% to 0.1%; the laptop network generator was too noisy for a trustworthy throughput claim.\n\nValidated with 501 router tests, framework type checks, and pickier lint.

Author: chrisbbreuer

storage/framework/core/router/src/stacks-router.ts

@@ -2904,7 +2904,7 @@ function formatResult(result: unknown, req: EnhancedRequest): Response {
     // CursorPaginator, emit `Link: <prev>; rel="prev", <next>; rel="next"`
     // alongside the JSON body — HATEOAS for REST clients + crawlers
     // who'd otherwise have to dig through the body to find next/prev.
-    const linkHeader = buildPaginatorLinkHeader(result)
+    const linkHeader = 'data' in result ? buildPaginatorLinkHeader(result) : null
     return formatJsonResult(result, req, linkHeader)
   }