Marks app paths in dev as supporting dynamic html

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

@@ -1317,6 +1317,11 @@ export default abstract class Server<ServerOptions extends Options = Options> {
       opts.isBot = isBotRequest
     }
 
+    // In development, we always want to generate dynamic HTML.
+    if (opts.dev && opts.supportsDynamicHTML === false) {
+      opts.supportsDynamicHTML = true
+    }
+
     const defaultLocale = isSSG
       ? this.nextConfig.i18n?.defaultLocale
       : query.__nextDefaultLocale
@@ -1441,7 +1446,8 @@ export default abstract class Server<ServerOptions extends Options = Options> {
     let isRevalidate = false
 
     const doRender: () => Promise<ResponseCacheEntry | null> = async () => {
-      const supportsDynamicHTML = !(isSSG || hasStaticPaths)
+      // In development, we always want to generate dynamic HTML.
+      const supportsDynamicHTML = opts.dev || !(isSSG || hasStaticPaths)
 
       const match =
         pathname !== '/_error' && !is404Page && !is500Page

test/e2e/app-dir/app/app/dynamic/[category]/page.js

@@ -0,0 +1,16 @@
+import { cookies } from 'next/headers'
+
+const Page = async () => {
+  const result = cookies().get('session')?.value ? 'has cookie' : 'no cookie'
+  return <div id="cookie-result">{result}</div>
+}
+
+export const generateStaticParams = async () => {
+  return [{ category: 'frameworks' }]
+}
+
+export const dynamic = 'force-dynamic'
+export const dynamicParams = true
+export const revalidate = 60
+
+export default Page

test/e2e/app-dir/app/index.test.ts

@@ -749,6 +749,28 @@ createNextDescribe(
             '{"category":"books","id":"hello-world"}'
           )
         })
+
+        it('should allow dynamic routes to access cookies', async () => {
+          for (const category of ['books', 'frameworks']) {
+            for (let i = 0; i < 2; i++) {
+              let $ = await next.render$(
+                `/dynamic/${category}`,
+                {},
+                {
+                  headers: {
+                    cookie: 'session=value',
+                  },
+                }
+              )
+
+              expect($('#cookie-result').text()).toBe('has cookie')
+
+              $ = await next.render$(`/dynamic/${category}`)
+
+              expect($('#cookie-result').text()).toBe('no cookie')
+            }
+          }
+        })
       })
 
       describe('catch-all routes', () => {