fix(rust/parametric): report effective propagation style in /trace/config

[bm1549]

Motivation

The Rust parametric app's GET /trace/config reported the propagation style from the extract-specific config only, so a global-only style — including one fed by OTEL_PROPAGATORS or a bare DD_TRACE_PROPAGATION_STYLE — was reported as empty. This is the companion to DataDog/dd-trace-rs#271, which adds OTEL_PROPAGATORS support to dd-trace-rs.

Changes

format_trace_propagation_extract in the Rust parametric app now falls back to the global propagation style when the extract-specific style is unset, mirroring the library's effective-extractor resolution (propagation/config.rs::get_extractors): extract-specific styles if set, otherwise the global style. One function, four added lines.

Verified locally with cargo check against a linked dd-trace-rs source (the type signatures compose: both getters return Option<&[TracePropagationStyle]>).

Workflow

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   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

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Reviewer checklist

• Anything but tests/ or manifests/ is modified ? I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added, removed or renamed?
  • Get a review from R&P team

🤖 Generated with Claude Code

[github-actions]

CODEOWNERS have been resolved as:

utils/build/docker/rust/parametric/src/datadog/dto.rs                   @DataDog/apm-rust @DataDog/system-tests-core

[datadog-official]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

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