Aari c24bf383e5
fix(gateway): expose the run metadata header to split-origin clients (#4535)
A browser client served from a different origin than the Gateway never
learns the id of the run it just created, so a brand-new thread keeps its
placeholder route for the whole session and every action gated on an
established thread — edit and rerun, regenerate, branch — stays hidden
until the page is reloaded.

Run-creating routes return the run's id in `Content-Location`, and the
LangGraph SDK resolves run metadata from that header alone. It is not
CORS-safelisted, so a cross-origin response hides it from JS unless the
server lists it in `Access-Control-Expose-Headers`. `useStream`'s
`onCreated` therefore never fires and the app cannot rewrite its route.

Expose it. `GATEWAY_CORS_ORIGINS` is a supported deployment mode, so the
CORS middleware has to carry everything that mode needs to read. Same-origin
nginx deployments are unaffected because CORS never applies to them.
2026-07-29 00:09:02 +08:00
..