Update check

packages/next/src/server/base-server.ts

@@ -1332,12 +1332,11 @@ export default abstract class Server<ServerOptions extends Options = Options> {
       }
 
       if (
-        !this.renderOpts.dev &&
-        (hasFallback ||
-          staticPaths?.includes(resolvedUrlPathname) ||
-          // this signals revalidation in deploy environments
-          // TODO: make this more generic
-          req.headers['x-now-route-matches'])
+        hasFallback ||
+        staticPaths?.includes(resolvedUrlPathname) ||
+        // this signals revalidation in deploy environments
+        // TODO: make this more generic
+        req.headers['x-now-route-matches']
       ) {
         isSSG = true
       } else if (!this.renderOpts.dev) {
@@ -1492,7 +1491,15 @@ export default abstract class Server<ServerOptions extends Options = Options> {
     if (isAppPath) {
       res.setHeader('vary', RSC_VARY_HEADER)
 
-      if (!isPreviewMode && isSSG && req.headers[RSC.toLowerCase()]) {
+      // We don't clear RSC headers in development since SSG doesn't apply
+      // These headers are cleared for SSG as we need to always generate the
+      // full RSC response for ISR
+      if (
+        !this.renderOpts.dev &&
+        !isPreviewMode &&
+        isSSG &&
+        req.headers[RSC.toLowerCase()]
+      ) {
         if (!this.minimalMode) {
           isDataReq = true
         }