traceparent header

traceparent: 00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01

Format: version-trace_id-parent_span_id-flags. 32-hex trace_id ties all spans together.

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Client injects

Span span = tracer.startSpan("a2a.tasks.send");
try (var scope = span.makeCurrent()) {
  request.header("traceparent", currentTraceParent());
  client.send(request);
}

Every ADK Java A2A client does this automatically via interceptor.

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Server extracts

Server reads incoming traceparent, uses as parent span for its work. Server's internal spans hang off client's trace.