## Summary
posthog-js sent product analytics to PostHog Cloud directly from the
browser. This points `api_host` at a same-origin `/ph` path that
forwards to PostHog Cloud EU server-side, following PostHog's standard
first-party reverse-proxy setup.
## How it works
A resource route forwards each request server-side, splitting by path:
`/ph/static/*` and `/ph/array/*` go to the asset host, everything else
(analytics events, feature flags) goes to the ingest host. It rewrites
the `Host` header, strips the `/ph` prefix, and streams the response
back. Only PostHog's own cookies are forwarded, so the app session
cookie stays first-party. Upstream hosts default to PostHog Cloud EU,
overridable via `POSTHOG_INGEST_HOST` / `POSTHOG_ASSETS_HOST`.
It also sets `cross_subdomain_cookie` so a single PostHog session is
shared across the marketing site and app.
Verified locally: static assets return 200 from the EU asset host, and
analytics events return 200 through the ingest host.
DKP
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