Link to the code that reproduces this issue

https://github.com/mariusch/nextjs-sa-ppr-repro

To Reproduce

1. next.config.ts: set output: "standalone" and cacheComponents: true
2. Create a dynamic route with a <Suspense> boundary (so PPR activates) and a Server Action
3. next build && node .next/standalone/server.js
4. Invoke the Server Action
5. Response is an HTML prerender shell instead of RSC payload → client throws E394

Current vs. Expected behavior

Server Action POST response headers after upgrading 16.1.7 → 16.2.0:

Both include x-nextjs-prerender: 1. Request includes Next-Action header in both cases.

Expected: Returns text/x-component with RSC payload.
Actual: Returns PPR HTML shell. Action executes, but client can't parse the response → E394.

Downgrading to 16.1.7 resolves it.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
Binaries:
  Node: 22.15.0
Relevant Packages:
  next: 16.2.0 (works on 16.1.7)
  react: 19.2.4
  react-dom: 19.2.4
  typescript: 5.9.3
Next.js Config:
  output: standalone

Which area(s) are affected? (Select all that apply)

cacheComponents, Server Actions, Partial Prerendering (PPR)

Which stage(s) are affected? (Select all that apply)

Other (Deployed), next start (local)

Additional context

Self-hosted via Docker (node:25-alpine), not Vercel. Azure Front Door in front but unchanged between versions.