fix(prod-server): serve static files for beforeFiles rewrite targets

Add static file serving for beforeFiles rewrite targets in the Pages
Router production server. This matches Next.js behavior where beforeFiles
rewrites can resolve to static files in public/ or other filesystem paths.

The fix passes middleware headers (including Set-Cookie) to the static
file response, ensuring middleware-set headers appear on static assets.

This resolves the issue from PR cloudflare#776 where beforeFiles rewrites that
target static files were not being served correctly.

Author: yunus25jmi1

packages/vinext/src/server/prod-server.ts

@@ -1563,6 +1563,9 @@ async function startPagesRouterServer(options: PagesRouterServerOptions) {
       }
 
       // ── 7. Apply beforeFiles rewrites from next.config.js ─────────
+      // Serve static files for beforeFiles rewrite targets. This matches
+      // Next.js behavior where beforeFiles rewrites can resolve to static
+      // files in public/ or other direct filesystem paths.
       if (configRewrites.beforeFiles?.length) {
         const rewritten = matchRewrite(resolvedPathname, configRewrites.beforeFiles, postMwReqCtx);
         if (rewritten) {
@@ -1573,6 +1576,22 @@ async function startPagesRouterServer(options: PagesRouterServerOptions) {
           }
           resolvedUrl = rewritten;
           resolvedPathname = rewritten.split("?")[0];
+
+          // Try serving static file at the rewritten path
+          if (
+            path.extname(resolvedPathname) &&
+            (await tryServeStatic(
+              req,
+              res,
+              clientDir,
+              resolvedPathname,
+              compress,
+              staticCache,
+              middlewareHeaders,
+            ))
+          ) {
+            return;
+          }
         }
       }