Adds Prometheus instrumentation across the checkout funnel, auth flow,
Stripe calls, rate limiters, and HTTP middleware (inflight gauge, request
and response sizes). Introduces a slog handler that counts log lines by
level so the dashboard can show error/warn rates; existing log.Printf
calls are routed through slog and counted as info.
Backs the new "terminalshop — Service Overview" Grafana dashboard.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Default prometheus.DefBuckets bottoms out at 5ms, which made every
route's p95 collapse to 4.75ms (histogram_quantile interpolation
within the smallest bucket). Custom buckets from 100µs to 5s now
distinguish microsecond-fast routes (health) from slower ones
(stripe-backed cart endpoints).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Adds Counter (http_requests_total) and Histogram
(http_request_duration_seconds) labeled by method, chi route pattern,
and status. Wired through a new Metrics middleware (after Recovery so
panics-turned-500s are still counted) and an unauthenticated /metrics
endpoint at the root for Prometheus to scrape.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
