Module metrics 

Prometheus metrics recorder and renderer.

The server installs a single global Prometheus recorder at startup via init, then exposes the gathered metrics over a /metrics route that calls render. Emitting code anywhere in the workspace uses the lightweight metrics facade (metrics::counter!, metrics::histogram!); when no recorder is installed (stdio mode, CLI, tests) those macros are cheap no-ops, so emitting metrics is always safe.

Everything here is fail-soft: a metrics problem must never take the server down, so install failures are logged and swallowed and /metrics simply reports “not initialized” until a recorder exists.

Functions

init

Install the global Prometheus recorder. Idempotent: a second call is a no-op, and a failed install is logged rather than propagated so startup continues.

is_installed

Whether a recorder has been installed. Primarily for tests and diagnostics.

render

Render the current metrics in Prometheus text exposition format, or None if no recorder has been installed (so the route can answer 503).