Baggage header not propagated on outgoing WebClient (Reactor Netty) requests

[ls-adrian-chong]

Summary

dd-trace-java does not inject the W3C baggage header on outgoing HTTP requests made via Spring WebClient (Reactor Netty transport). Trace headers (traceparent, x-datadog-*) are injected correctly, but baggage is consistently missing.

Environment

• dd-java-agent: 1.62.0
• Java: 17 and 25 (Amazon Corretto) — tested both, same result
• Spring Boot: 3.4.13 and 3.5.14 — tested both, same result
• Reactor Netty: 1.2.6 and 1.2.17 — tested both, same result

Configuration

DD_TRACE_PROPAGATION_STYLE=tracecontext,baggage,datadog
DD_TRACE_INTEGRATION_REACTOR_HOOKS_ENABLED=true
OTEL_PROPAGATORS=tracecontext,baggage

Also tried via JVM properties:

-Ddd.trace.propagation.style.extract=tracecontext,baggage,datadog
-Ddd.trace.propagation.style.inject=tracecontext,baggage,datadog
-Ddd.trace.integration.reactor-hooks.enabled=true

Reproduction

Minimal Spring Boot app with a single endpoint that receives a baggage header and proxies via WebClient:

@GetMapping("/proxy-netty")
public String proxyNetty() {
    return WebClient.builder().build()
        .get()
        .uri("http://localhost:9090/downstream")
        .retrieve()
        .bodyToMono(String.class)
        .block();
}

Steps:

1. Start an echo server on port 9090 (prints received headers)
2. Start the app with dd-java-agent attached
3. Send: curl -H "baggage: userId=12345,sessionId=abc" http://localhost:8080/proxy-netty
4. Observe echo server output

Expected: Echo server receives baggage: userId=12345,sessionId=abc
Actual: Echo server receives traceparent and x-datadog-* headers but no baggage

Notes

• The same baggage header IS propagated correctly when using RestClient with JdkClientHttpRequestFactory or raw java.net.http.HttpClient.
• This suggests the issue is specific to the Reactor Netty instrumentation path.