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tRPC

Tracing

Client spans that propagate traceparent and b3, so client and server share one trace.

Tracing is opt-in: install an Effect tracer and every call runs in a span named trpc.<path> (kind client), with rpc.method, trpc.type and trpc.error.code on failure. httpLink sends the span as traceparent and b3 headers (wsLink and experimental_messagePortLink put them in each request message's trace field), and the server's trpc.<path> span joins the same trace (Server tracing):

import { NodeSdk } from '@effect/opentelemetry';

const program = client.post.byId
  .query({ id })
  .pipe(Effect.withSpan('page.load'));
await Effect.runPromise(program.pipe(Effect.provide(NodeSdk.layer(otel))));

With no tracer (the Promise client, or Effect's default), calls open no span and send no headers or trace fields, so they cost nothing and simple requests stay free of CORS preflights. Effect.provideService(Tracer.DisablePropagation, true) keeps the spans and drops the headers.

On Cloudflare, see Workers Traces.