TraceContext class

Correlation identifiers for one request, ambient for its whole lifetime.

A request id that only exists as a header dies at the first hop: a call the handler makes to another service opens a fresh, uncorrelated request, and the two services' logs cannot be joined afterwards. This carries the identifiers in the zone instead, so anything running inside the request — a logger, a repository, an outbound client — can reach them without being handed them explicitly.

final id = TraceContext.current?.requestId;

Sending them on is outboundHeaders. Nothing does that automatically: what counts as a trusted peer is the app's call, not the framework's, and forwarding correlation headers to an arbitrary third party is a small information leak.

This deliberately propagates traceparent rather than creating spans. A collector that already understands W3C Trace Context keeps working, and a service that sits between two instrumented ones stops breaking the chain — without this package taking on span lifecycles, samplers or exporters.