Fix continuation leakage on netty http2 client pipeline

[amarziali]

What Does This Do

Fixes an orphaned async continuation in Netty 4.1 HTTP/2 client flows.

For HTTP/1, the connect continuation captured in ConnectAdvice is later consumed by the request handler. In HTTP/2 prior-knowledge mode, the continuation is captured on the connection channel but requests are written on stream channels, so the continuation was never consumed or canceled.

This change marks channels that have an HTTP/2 connection codec as HTTP/2 connections and skips capturing the connect continuation for them. This avoids creating a continuation with no consumer. The request handler now also checks the parent channel for an existing connect continuation, covering stream-channel request paths where a parent-channel continuation is valid.

Issue spotted using an experimental continuation lifecycle tracker that gave:

continuation #35 captured-never-activated-or-canceled
    captured by: captureActiveSpan
    span: parent trace_id=9 span_id=8
    capture thread: reactor-http-nio-6
    activations=0, closed_scopes=0, cancels=0
    capture stack:
      at io.netty.channel.DefaultChannelPipeline.connect(DefaultChannelPipeline.java:978)
      at io.netty.channel.AbstractChannel.connect(AbstractChannel.java:253)
      at reactor.netty.transport.TransportConnector.lambda$doConnect$3(TransportConnector.java:149)
      at io.netty.util.concurrent.PromiseTask.runTask(PromiseTask.java:98)

Motivation

Additional Notes

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Jira ticket: [PROJ-IDENT]

[datadog-prod-us1-3]

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⚠️ Warnings

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[chatgpt-codex-connector]

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[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	13.92 s	13.88 s	[-0.6%; +1.1%] (no difference)
startup:insecure-bank:tracing:Agent	12.86 s	12.90 s	[-1.3%; +0.7%] (no difference)
startup:petclinic:appsec:Agent	16.18 s	15.92 s	[-10.6%; +13.9%] (unstable)
startup:petclinic:iast:Agent	16.23 s	16.76 s	[-11.8%; +5.6%] (unstable)
startup:petclinic:profiling:Agent	16.46 s	16.07 s	[-6.3%; +11.1%] (unstable)
startup:petclinic:sca:Agent	15.96 s	16.45 s	[-11.8%; +5.8%] (unstable)
startup:petclinic:tracing:Agent	15.93 s	15.40 s	[-5.0%; +11.8%] (unstable)

Commit: b1ed4c77 · CI Pipeline · Benchmarking Platform UI

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[chatgpt-codex-connector]

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Reviewed commit: b1ed4c778c

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