Add verified PostHog readership analytics

[jacobra19]

Implements the analytics integration for #32. The production site currently delivers Vercel Analytics events but blocks Google Analytics collection through its CSP; this adds direct browser-to-PostHog readership tracking while retaining both existing trackers until replacement production data is verified.

Changes

• Capture one pageview on initial load and each pathname navigation, referral/UTM attribution, outbound clicks, 30 seconds of visible article time, and 50%/90% article scroll milestones.
• Exclude development, preview, localhost, and opted-out author traffic. Disable replay and automatic interaction capture; strip query strings and hashes from captured URLs.
• Allow the PostHog ingestion origin in the existing CSP, without Vercel Functions or rewrites. GA repair and HTTP-header hardening remain scoped to Fix CSP so Google Analytics requests are not blocked in production #20 and Move CSP and security hardening to HTTP response headers #21.
• Add browser tests, a production CSP/network audit script, documented event definitions and author opt-out, and reproducible queries for the six-view readership dashboard.

The checked-in phc_ token is the public browser ingestion token, not a personal API key.

Validation

• yarn validate:content and yarn build passed.
• yarn test:e2e: 12 passed, 10 intentionally skipped (desktop-only checks and opt-in live ingestion).
• Explicit live-ingestion test passed: six labeled QA events arrived in PostHog with the expected page paths, article title, scroll thresholds, engagement duration, outbound destination, and replay disabled. Dashboard queries exclude these QA events.
• Production browser audit confirmed Vercel collection returned HTTP 200 and GA collection was blocked by the existing CSP.

Rollout

Ingestion was verified using the production build in an isolated browser; this change has not yet been deployed. After merge/deployment, follow docs/analytics.md to verify the deployed CSP and event delivery, then compare readership data before consolidating trackers. Keep #32 open until that production verification is complete.

[vercel]

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Project	Deployment	Actions	Updated
yakov-dev	Ready	Preview	Sep 21, 2026 9:01pm UTC