Support W3C baggage propagation across reactor-netty connect hand-off

[mcculls]

What Does This Do

Support W3C baggage propagation across reactor-netty connect hand-off

Motivation

The connect-span path carried only the active AgentSpan across the subscription -> I/O thread hand-off, dropping the rest of the Datadog Context (including baggage). Capture the full Context instead and build the continuation directly via Context.capture().

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Jira ticket: [PROJ-IDENT]

[mcculls]

@codex review

[Copilot]

Pull request overview

This PR fixes loss of W3C baggage during the Reactor Netty “connect” subscription → I/O thread hand-off by propagating the full Datadog Context (not just the active span) and capturing the continuation from that context.

Changes:

• Store the full Datadog Context in Reactor’s ContextView during connect setup.
• Build the connect-parent continuation via Context.capture() and transfer it to the Netty channel attribute.
• Add a regression test asserting the outgoing request includes the W3C baggage header.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
dd-java-agent/instrumentation/reactor-netty-1.0/src/main/java/datadog/trace/instrumentation/reactor/netty/CaptureConnectSpan.java	Captures and stores the full Datadog Context (instead of only activeSpan()) into the Reactor context for the connect path.
dd-java-agent/instrumentation/reactor-netty-1.0/src/main/java/datadog/trace/instrumentation/reactor/netty/TransferConnectSpan.java	Transfers a ContextContinuation created from the captured Context onto the Netty channel attribute, preserving baggage and other context entries.
dd-java-agent/instrumentation/reactor-netty-1.0/src/test/java/ReactorNettyBaggagePropagationTest.java	Adds a regression test verifying W3C baggage header propagation on an outgoing Reactor Netty request.

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Reviewed commit: 3c15da8bd2

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[datadog-datadog-prod-us1]

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 65.66% (+8.27%)

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[datadog-datadog-prod-us1]

More details

The PR correctly fixes W3C baggage propagation across reactor-netty's thread hand-off by capturing the full Context instead of just the active span. This ensures baggage (and any other context data) survives the subscription → I/O thread transition. The new test validates baggage appears in outgoing request headers. The fix improves on the old code by also handling baggage-only scenarios.

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