remove next-action header when following a redirect (#65615)

When a server action performs a redirect, we send an RSC request to the
redirect URL so that everything can be handled in a single roundtrip.

However, we forward the `next-action` header to that request. This means
that the intra-app RSC request will be incorrectly associated with an
action, and any rewrites we do for `next-action` requests (such as the
work in the Next.js builder to ensure actions are routed to streaming
outputs) won't be handled correctly.

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packages/next/src/server/app-render/action-handler.ts

@@ -8,6 +8,8 @@ import type { BaseNextRequest, BaseNextResponse } from '../base-http'
 import {
   RSC_HEADER,
   RSC_CONTENT_TYPE_HEADER,
+  NEXT_ROUTER_STATE_TREE,
+  ACTION,
 } from '../../client/components/app-router-headers'
 import { isNotFoundError } from '../../client/components/not-found'
 import {
@@ -292,7 +294,10 @@ async function createRedirectRenderResult(
     }
 
     // Ensures that when the path was revalidated we don't return a partial response on redirects
-    forwardedHeaders.delete('next-router-state-tree')
+    forwardedHeaders.delete(NEXT_ROUTER_STATE_TREE)
+    // When an action follows a redirect, it's no longer handling an action: it's just a normal RSC request
+    // to the requested URL. We should remove the `next-action` header so that it's not treated as an action
+    forwardedHeaders.delete(ACTION)
 
     try {
       const response = await fetch(fetchUrl, {

test/e2e/app-dir/actions/app-action.test.ts

@@ -1310,6 +1310,24 @@ describe('app-dir action handling', () => {
       expect(await browser.elementByCss('h1').text()).toBe('foo=; bar=2')
     })
 
+    it('should not forward next-action header to a redirected RSC request', async () => {
+      const browser = await next.browser('/redirects/action-redirect')
+
+      await browser.elementById('redirect-with-search-params').click()
+      await retry(async () => {
+        expect(await browser.url()).toMatch(
+          /\/redirects\/action-redirect\/redirect-target\?baz=1/
+        )
+      })
+      // verify that the search params was set correctly
+      expect(await browser.elementByCss('h2').text()).toBe('baz=1')
+
+      // we should not have the next-action header in the redirected request
+      expect(next.cliOutput).not.toContain(
+        'Action header should not be present'
+      )
+    })
+
     it.each(['307', '308'])(
       `redirects properly when server action handler redirects with a %s status code`,
       async (statusCode) => {

test/e2e/app-dir/actions/app/redirects/action-redirect/redirect-target/page.js

@@ -1,8 +1,12 @@
-import { cookies } from 'next/headers'
+import { cookies, headers } from 'next/headers'
 
 export default function Page({ searchParams }) {
   const foo = cookies().get('foo')
   const bar = cookies().get('bar')
+  const actionHeader = headers().get('next-action')
+  if (actionHeader) {
+    throw new Error('Action header should not be present')
+  }
   return (
     <div>
       <h1>