fix(answer): stash the answer input event before addToolOutput

The onSubmitAnswer path was the one Wave B send site missing its stash:
addToolOutput triggers the SDK's automatic continuation send, the
transport found nothing stashed, and threw — the answer never POSTed, so
the question stayed open. One line (plus the contract comment). Caught
live by the owner; the suite drives answer events directly at the
handler, so this client seam stays untested until Wave D's client work.

next-env.d.ts

@@ -1,7 +1,7 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-import "./.next/types/routes.d.ts";
-import "./.next/types/root-params.d.ts";
+import "./.next/dev/types/routes.d.ts";
+import "./.next/dev/types/root-params.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.