Goal

Integrate PostHog across the new Next.js website and calculator-app surfaces so we have:

• product analytics for the calculator
• website funnel/content analytics
• stronger client and server error tracking
• production-ready ingestion through app-local proxying
• release-aware configuration for source maps and monitoring

Scope

• Bootstrap posthog-js in both Next apps.
• Add shared calculator analytics helpers and typed event schemas in app/src.
• Instrument core calculator flows:
  • report builder opened/started/created
  • report-builder configuration choices
  • household builder interactions
  • calculation lifecycle
  • report output views and output actions
• Instrument key website flows:
  • enter-calculator CTA
  • newsletter signup
  • research filter/article interactions
  • country switching
• Add robust error capture:
  • shared React boundary capture
  • Next error.tsx and global-error.tsx
  • server-side request error capture
• Proxy PostHog traffic through Next rewrites.
• Add release/source-map related configuration and env documentation.

Acceptance Criteria

• website and calculator-app both initialize PostHog from official Next.js integration points.
• Calculator events are queryable for builder selection, report creation, calculations, and output usage.
• Website events are queryable for CTA/content/signup interactions.
• Client, route, and server exceptions are visible in PostHog with useful metadata.
• PostHog traffic is routed through app-local proxy paths instead of direct third-party ingestion URLs.
• The apps build successfully with the project’s supported Node version.