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	13.98 s	14.02 s	[-1.2%; +0.7%] (no difference)
startup:insecure-bank:tracing:Agent	12.97 s	13.02 s	[-1.2%; +0.5%] (no difference)
startup:petclinic:appsec:Agent	17.60 s	17.53 s	[-0.3%; +1.2%] (no difference)
startup:petclinic:iast:Agent	17.35 s	17.55 s	[-1.9%; -0.4%] (maybe better)
startup:petclinic:profiling:Agent	17.41 s	17.12 s	[+0.6%; +2.9%] (maybe worse)
startup:petclinic:sca:Agent	17.71 s	17.51 s	[+0.0%; +2.3%] (maybe worse)
startup:petclinic:tracing:Agent	16.56 s	16.15 s	[-1.9%; +6.8%] (no difference)

Commit: a6910415 · 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]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 397a1ff69a

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".

[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.

Was this helpful? React 👍 or 👎

_{Open Bits AI session}

_{🤖 Datadog Autotest · Commit 397a1ff · What is Autotest? · @DataDog review to ask questions · Any feedback? Reach out in #autotest}

[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.

Dismissing stale review

[Copilot]

🟡 Changes recommended

The core round-trip behavior lacks coverage, and parsing introduces an avoidable hot-path allocation.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Separates the OpenTelemetry ot tracestate member for future sampling support while preserving its opaque value and position.

Changes:

• Extracts and stores ot member metadata.
• Re-emits ot in its inherited position.
• Copies parsed state across propagation contexts.

File summaries

File	Description
OtelTraceStateParsingTest.java	Tests the new state container.
W3CPTagsCodec.java	Extracts and rebuilds ot members.
PTagsFactory.java	Stores and transfers parsed state.
OtelTraceState.java	Defines the opaque state representation.
PropagationTags.java	Adds state-copying API.
HttpCodec.java	Uses state-aware copying during extraction.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 2
• Review effort level: Balanced

---

💡 Configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[mcculls]

Note the new muzzle failure happens on master too - it will be unblocked once #12478 is merged

[mcculls]

I think this is ready to be merged now - thanks for the continual improvements to this PR, and the extra tests.

Note I'm going to add a task to revisit this parser in the future to think about ways it could be refactored to simplify the overall structure/logic, but that's separate to this feature