feat(deploy): harden production proxy and cron configuration

docs/deployment-production.md

@@ -57,6 +57,34 @@ Before deploying, set production-safe values in `.env` (using `.env.example` as
 
 Keep secrets out of source control.
 
+## Reverse proxy assumptions (Nginx Proxy Manager)
+
+This app is expected to run behind a reverse proxy in production.
+
+- TLS is terminated at the proxy.
+- Proxy forwards standard host/protocol headers (`Host`, `X-Forwarded-Proto`, `X-Forwarded-Host`).
+- Public origin is configured explicitly with `NEXT_PUBLIC_APP_URL`.
+
+To keep callback behavior stable behind proxy layers, auth redirect responses use the configured application origin from environment configuration rather than relying only on request host detection.
+
+## Callback URL expectations
+
+- `NEXT_PUBLIC_APP_URL` must be set to the public HTTPS URL used by users.
+- Supabase auth redirect/callback configuration must allow:
+  - `<NEXT_PUBLIC_APP_URL>/auth/callback`
+
+The callback route also validates the `next` parameter as an internal path to prevent unsafe external redirects.
+
+## Cron protection expectations
+
+Operational cron endpoints are protected with a shared secret.
+
+- Required header: `x-cron-secret`
+- Server secret source: `CRON_SHARED_SECRET`
+- Backward compatibility fallback: `CRON_SECRET`
+
+For new production setups, set `CRON_SHARED_SECRET` and use that value for all cron callers.
+
 ## Jenkins pipeline flow
 
 The repository includes a declarative `Jenkinsfile` with the following stages: