When a Server Action is called from a page under an intercepting modal in a parallel slot, Next.js forwards it with an internal fetch() to the route that owns the action. On Vercel, that forwarded request goes to the current production deployment, not to the client's pinned deployment, so clients on an older deployment get UnrecognizedActionError (409) after every deploy.

Minimal reproduction (Next.js 16.4.2), with steps, expected and actual results, and request IDs from a live run: https://github.com/gzucca/skew-forwarded-action-repro

Live deployment: https://skew-forwarded-action-repro.vercel.app

Vercel support confirmed that x-deployment-id is not honored on requests that a function sends, and suggested we raise it here. Proposed fix: have Next.js send the forwarded request to the originating deployment's own URL, or have the edge honor the pin on requests that a function sends to its own project.