OpenTelemetry (id_effect_opentelemetry)

The workspace crate id_effect_opentelemetry implements Phase B of the Effect.ts parity plan: first-class OpenTelemetry traces and metrics alongside id_effect’s fiber-local with_span and Metric primitives.

Design goals match @effect/opentelemetry:

• Opt-in at the dependency boundary — the core id_effect crate does not depend on OTEL.
• Tracing — bridge tracing spans to OTEL exporters (OTLP in production; in-memory in tests).
• Propagation — W3C Trace Context (traceparent / tracestate) on portable header maps.
• Metrics — dual-write bridges from Metric counters and duration histograms to OTEL instruments.

Tracing: compose with_span and OTEL

Use id_effect_opentelemetry::with_span_otel when you want both:

1. Fiber-local span stack and EffectEvent stream (id_effect::with_span), and
2. A tracing span exported through tracing_opentelemetry.

Build a tracer provider (here: in-memory for tests), install a tracing subscriber with an OTEL layer, then run effects under with_span_otel:

#![allow(unused)]
fn main() {
use id_effect::{install_tracing_layer, run_blocking, succeed, TracingConfig};
use id_effect_opentelemetry::{
  sdk_tracer_provider_with_in_memory_exporter, trace_subscriber_for_provider, with_span_otel,
};
use opentelemetry_sdk::trace::InMemorySpanExporter;

let exporter = InMemorySpanExporter::default();
let provider = sdk_tracer_provider_with_in_memory_exporter(&exporter);
let subscriber = trace_subscriber_for_provider(&provider, false);

tracing::subscriber::with_default(subscriber, || {
  let _ = run_blocking(install_tracing_layer(TracingConfig::enabled()), ());
  let eff = with_span_otel("request", succeed::<(), (), ()>(()));
  let _ = run_blocking(eff, ());
});

let _ = provider.force_flush();
let _ = provider.shutdown();
}

In production you typically:

1. Configure an OTLP exporter (or another SpanExporter) on SdkTracerProvider.
2. Call register_global_tracer_provider once at startup.
3. Install a global tracing_subscriber stack with tracing_opentelemetry::layer().

W3C Trace Context on header maps

For HTTP clients built on Vec<(String, String)> (or similar), use:

• install_w3c_trace_context_propagator once per process.
• inject_trace_context_into_headers before sending a downstream request.
• extract_trace_context_from_headers when handling an incoming request.

For Axum / http::HeaderMap, map headers into this shape at the boundary or add a small adapter in your app.

Metrics: CounterBridge and DurationHistogramBridge

CounterBridge and DurationHistogramBridge keep id_effect::Metric snapshots for tests while exporting measurements to OTEL.

Create an SdkMeterProvider with a PeriodicReader and an InMemoryMetricExporter for CI-style assertions, or wire an OTLP metrics exporter for production.

Cardinality: keep label sets small and stable; prefer bounded service, route, tenant keys over high-cardinality user IDs in metric attributes.

Axum + Tokio production sketch

1. Build tracer + meter providers with OTLP endpoints from id_effect_config (or env).
2. Register globals and try_init a tracing_subscriber registry (fmt + OTEL + optional EnvFilter).
3. In Axum middleware, extract traceparent into an OTEL Context, attach it to the request extension, and spawn handler work inside that context.
4. On graceful shutdown, call force_flush / shutdown on providers (mirror Scope finalizer patterns from id_effect).

See also: docs/effect-ts-parity/phases/phase-b-opentelemetry.md in the repository for the full task breakdown and Beads slug map.