Prefer Lambda X-Ray trace header from carrier

[akg268]

Fixes open-telemetry/opentelemetry-java-instrumentation#15517

This updates the AWS X-Ray Lambda propagator to prefer the Lambda trace header from the extraction carrier under com.amazonaws.xray.traceHeader before falling back to the system property and _X_AMZN_TRACE_ID.

It preserves the existing regular X-Ray propagator behavior and keeps the Lambda-only active tracing path scoped to the Lambda propagator.

Validation: previous CI on the same code path was green; this replacement PR uses the same branch contents after the branch rename.

[akg268]

Hi @srprash @wangzlei, I opened this replacement PR from a clean branch name. It carries the same Lambda X-Ray propagator update as the earlier green PR and pairs with open-telemetry/opentelemetry-java-instrumentation#19920.

[Copilot]

Pull request overview

Updates the AWS X-Ray Lambda propagator to first look for the Lambda trace header in the extraction carrier under com.amazonaws.xray.traceHeader (including a lowercase variant) before falling back to the system property and _X_AMZN_TRACE_ID. This keeps the active-tracing Lambda-specific behavior isolated to AwsXrayLambdaPropagator while leaving the regular AwsXrayPropagator unchanged.

Changes:

• Prefer carrier-provided com.amazonaws.xray.traceHeader during extraction, falling back to system property and environment variable.
• Support lowercase carrier key lookup (com.amazonaws.xray.traceheader) to match common header normalization behavior.
• Add unit tests covering precedence, lowercase lookup, and link behavior when both the standard X-Ray header and Lambda trace header are present.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
aws-xray-propagator/src/main/java/io/opentelemetry/contrib/awsxray/propagator/AwsXrayLambdaPropagator.java	Adds carrier-first lookup (plus lowercase fallback) before reading system property / env var.
aws-xray-propagator/src/test/java/io/opentelemetry/contrib/awsxray/propagator/AwsXrayLambdaPropagatorTest.java	Adds tests verifying new precedence behavior, lowercase carrier key support, and link/parent interactions.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.