refactor(propagation): Parse OpenTelemetry tracestate member

[MilanGarnier]

What Does This Do

Refactors W3C tracestate handling so the OpenTelemetry ot member is
represented separately while its value remains opaque.

• Extracts and re-emits the raw ot member.
• Preserves its inherited position when rebuilding tracestate.
• Does not interpret rv or th or connect the member to sampling.

Motivation

Isolate the tracestate parsing foundation from the consistent-sampling
behavior added by the follow-up PR.

Additional Notes

This is the first PR in a two-PR stack. The sampling behavior follows in
#12397.

Validation:

• :dd-trace-core:compileJava
• :dd-trace-core:spotlessCheck
• git diff --check

Contributor Checklist

• Format the title according to the contribution guidelines.
• Assign the required type: and comp: labels.
• Keep sampling behavior and tests in the follow-up PR.

Jira ticket: APMAPI-2171

[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	14.77 s	14.68 s	[-0.4%; +1.5%] (no difference)
startup:insecure-bank:tracing:Agent	13.56 s	13.66 s	[-1.6%; +0.1%] (no difference)
startup:petclinic:appsec:Agent	17.62 s	17.40 s	[+0.5%; +2.1%] (maybe worse)
startup:petclinic:iast:Agent	17.47 s	17.48 s	[-0.7%; +0.6%] (no difference)
startup:petclinic:profiling:Agent	17.04 s	17.23 s	[-5.6%; +3.3%] (no difference)
startup:petclinic:sca:Agent	17.64 s	17.44 s	[+0.1%; +2.2%] (maybe worse)
startup:petclinic:tracing:Agent	16.47 s	16.67 s	[-2.6%; +0.1%] (no difference)

Commit: db321c06 · CI Pipeline · Benchmarking Platform UI

---

Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.

[chatgpt-codex-connector]

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[datadog-datadog-prod-us1]

More details

The change keeps the raw ot member and its inherited position when it rebuilds tracestate. The static review finds no reportable regression in the changed parsing and serialization paths.

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[mcculls]

The double-parsing issue will need to be fixed before this can be merged.

Claude suggests giving PTags a way to accept an already-built OtelTraceState directly (e.g. setOtelTraceState), and have applyTraceContextToFirstContext pass the parsed object from traceContext.getPropagationTags() instead of round-tripping through the string.

The double-counting issue is easily solved by removing the second addition.