13 — Observability and Growth

Tiered PostHog+Sentry+GA4 stacks wired from day one; feature flags, PLG patterns, incident auto-remediation.

Instrumentation tiers

Per _kernel/standards.md#integrations:

• Tier 1 (solo) — PostHog + Workers Tracing OTLP (2 vendors max, cookie-free, free tier covers <10k MAU)
• Tier 2 (enterprise) — + Sentry @sentry/cloudflare v9 + GA4/GTM + Axiom
• Tier 3 (LLM-heavy >10k calls/mo) — + AI Gateway

PostHog (Tier 1 cornerstone)

• Snippet on every HTML page w/ persistence:'memory' (cookie-free); capture_pageview + capture_pageleave + autocapture:true
• Unified platform: product analytics + feature flags + session replay + error tracking
• CSP: script-src + connect-src for posthog domain
• Per-feature event naming: <feature>:<action> (signup:complete, editor:save, share:copy)

Sentry (Tier 2)

• @sentry/cloudflare v9 + withSentry wrapper; project via mcp__sentry__create_project (org:megabyte-labs)
• SENTRY_DSN via wrangler secret put
• Pattern: withSentry(env => ({ dsn, tracesSampleRate: 1.0, sendDefaultPii: false }), worker)
• Breadcrumbs before risky ops; capture exception w/ context tags (worker | route | userId)
• Release tracking via SENTRY_RELEASE env; Workers Tracing handles I/O spans

Workers Tracing (Tier 1 + 2) / GA4 + GTM (Tier 2) / AI Gateway (Tier 3)

• Workers Tracing: [observability] enabled = true in wrangler.jsonc — zero-config OTel I/O tracing; export to Axiom, Honeycomb, Grafana, Datadog via @opentelemetry/exporter-trace-otlp-http
• GA4 + GTM: container snippet (head script + noscript iframe); CSP: googletagmanager.com + google-analytics.com + analytics.google.com + region1.google-analytics.com; server-side tagging for EU; custom dimensions over custom events
• AI Gateway: env.AI.run() auto-routes; direct Anthropic: https://gateway.ai.cloudflare.com/v1/{account}/{gateway}/anthropic/v1/messages; caching + rate-limit + fallback + per-call logging

Stripe (SaaS billing only — per rules/payments-routing.md)

• Webhook-first w/ idempotent processing (D1 dedupe table payment_events(event_id, source, processed_at) UNIQUE)
• Stripe-Signature HMAC + 5-min replay window
• Mint products + prices via MCP (idempotent via lookup_key); subscription state machine in D1
• STRIPE_WEBHOOK_SECRET via POST /v1/webhook_endpoints

Square (accept-money default — per rules/payments-routing.md)

• Square Web Payments SDK card form + Apple Pay + Google Pay + Cash App Pay
• Square-Signature HMAC-SHA256 w/ 6-hr replay window; idempotency_key UUID per request (24-hr dedupe)
• Nonprofit verified-501c3 discount (2.6%+10¢ vs 3.5%+15¢)

Listmonk (newsletter — self-hosted on Coolify)

• Amazon SES SMTP relay (LISTMONK_FROM_EMAIL); listmonkSendTx(env, { templateAlias, ... }) via KV-cached alias→id map
• Templates in emails/*.html synced via scripts/listmonk-sync.mjs
• Auth: Authorization: token <user>:<key> (Listmonk 3.x API-user pattern)

PLG 7-Layer Framework

1. Discovery — SEO + AI search + word-of-mouth + paid
2. Sign-up — passwordless preferred (Clerk M2M JWT)
3. Activation — first-value-in-X-min metric (aha moment per rules/feature-flags.md instrumentation)
4. Engagement — DAU/MAU ratio, session depth
5. Retention — D1/D7/D30 cohort
6. Revenue — upgrade trigger, expansion
7. Referral — viral coefficient, two-sided rewards

Programmatic SEO (5 page types)

• /integrations/{tool} · /compare/{a}-vs-{b} · /for/{audience} · /templates/{type} · /{city}-{service}
• Each: unique H1 + meta desc + 800+ unique words + 1 unique image + 3+ internal links + 1+ outbound citation. Cap 200 pages per axis.
• Per rules/copy-writing.md § pSEO + rules/thin-source-amplification.md.

GEO / AI search

• Quotable answer blocks 40-60 words (LLM citation magnet); FAQPage schema highest AI-citation rate (ChatGPT / Perplexity / Google AI Overviews)
• JSON-LD facts MUST also appear as visible HTML body text; lead paragraphs answer query in <40 words
• EEAT: author bio + Person schema + sameAs + dated revision + ownership statement
• llms.txt at site root (DX-only, <0.3% adoption — not build gate)

Local-business conversions + CRO

Track per local-conversions.md: phone_click (tel:) · direction_click (Google Maps) · form_submit · booking_click (Calendly/Cal.com) · chat_click · review_click (Google Business/Yelp). Each fires PostHog + Sentry breadcrumb + (Tier 2) GA4 conversion event.

CRO: sticky CTA bar on mobile · scroll-progress bar (subtle) · exit-intent modal (cart/pricing only, not blogs) · social proof near every CTA · urgency without dark patterns ("3 spots left this week" if true) · trust strip above fold · single primary CTA per surface.

Incident auto-remediation

Sentry → Inngest pipeline: (1) Sentry webhook on event.alert.triggered → (2) Inngest dispatches incident-responder agent → (3) agent reads event, traces to source file, proposes fix, opens PR via gh MCP → (4) PR auto-merges if all CI gates pass per rules/ai-seniority.md.

See submodules: posthog, ga4-gtm, sentry, stripe-billing, square-payments, listmonk, plg-framework, programmatic-seo, incident-remediation, geo-ai-search, local-conversions.