[posthog]

Problem

• Ad blockers can silently drop pageviews from www.lightcms.me. The traffic numbers are low by an unknown amount.
• posthog-js sends events directly to us.i.posthog.com, and vercel.json has no rewrites. Thus no production event goes through a proxy.
• On a developer-facing CMS, many visitors are likely to use ad blockers.

Origin

• Health checks
• Scout: signals-scout-general
• First signal: 2026-10-23
• Inbox report: open
• Task started by: auto-start, after the report was rated P3 and ready to fix

Changes

• Same-origin reverse proxy: the browser sends all PostHog traffic to /ingest on the site, and Vercel rewrites it to PostHog.

Path	Destination
/ingest/static/*	https://us-assets.i.posthog.com/static/*
/ingest/array/*	https://us-assets.i.posthog.com/array/* (remote config bundle)
/ingest/*	https://us.i.posthog.com/*

- api_host: "https://us.i.posthog.com",
+ api_host: "/ingest",
+ ui_host: "https://us.posthog.com",

• The project token does not change.
• vite.config.ts gets a matching server.proxy. Without it, vp dev would send capture requests to /ingest and get 404s.
• Locale routing does not intercept /ingest. The Vercel rewrites apply before the SvelteKit function runs, and ingest is not a locale, so reroute and handleI18n do not change the path.

Warning

Vercel bills proxied traffic as Fast Data Transfer and Edge Requests. Current traffic is low, so the cost is small. If session replay volume grows, the PostHog managed reverse proxy has no data transfer cost.

How to verify

• vp fmt --check and vp lint pass on the changed files.
• vp test run: 9 files, 105 tests pass.
• In vp dev, /ingest/static/array.js, /ingest/array/<token>/config.js and POST /ingest/flags return 200 through the proxy.
• Preview deploy: the network tab shows /ingest/e/ and /ingest/flags requests with status 200, and no requests to *.i.posthog.com.
• After production deploy: the proxied share of production pageviews goes from 0% to at least 90% in the first full 7 days. If production pageviews drop to zero, the proxy broke capture. Revert this PR.

Agent context

• I did not test the Vercel rewrites themselves in the sandbox. The rewrite syntax follows the PostHog Vercel proxy guide. The preview deploy is the first real test.
• I added the /ingest/array/* rule in addition to the two rules in the report, because posthog-js loads its remote config from that path.
• The sandbox checkout has a broken static/llms.txt symlink (the static/skills submodule is not checked out). To load the Vite config, I added a temporary local stub. I did not commit it.
• I did not run full vp check. On main, it already fails on unrelated files, so I ran format and lint on the changed files only.

---

Created with PostHog Desktop from this inbox report.

🤖 Generated with Claude Code

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
lightcms	Ready	Preview	Nov 12, 2026 7:30am UTC

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