ClientSignals.Plug (client_signals v0.4.3)

Reads the coarse, self-reported Fly-Client-* headers (as produced by ClientSignals.headers_for/2) off an incoming request and attaches them to the current request's OTel span as fly.client.* attributes.

This gives services a rough human-vs-agent traffic estimate for capacity planning and product decisions. These values are self-reported by the caller and must never be used for gating, enforcement, or any per-request trust decision.

This module is only defined when both :plug and :opentelemetry_api are loaded; both are optional dependencies of :client_signals.