Prefer Lambda X-Ray trace header from carrier

[akg268]

Summary

• read com.amazonaws.xray.traceHeader from the extraction carrier before falling back to the system property and _X_AMZN_TRACE_ID
• keep existing request X-Amzn-Trace-Id extraction behavior so it can still be used as a span link when active tracing provides the parent
• handle the lowercase carrier key used by the Java instrumentation map getter

Refs open-telemetry/opentelemetry-java-instrumentation#15517
Companion instrumentation PR: open-telemetry/opentelemetry-java-instrumentation#19438

Testing

• ./gradlew :aws-xray-propagator:test --tests io.opentelemetry.contrib.awsxray.propagator.AwsXrayLambdaPropagatorTest
• ./gradlew :aws-xray-propagator:spotlessCheck
• git diff --check

[Copilot]

Pull request overview

Updates the AWS X-Ray Lambda propagator to prefer the Lambda-specific X-Ray trace header (com.amazonaws.xray.traceHeader) from the extraction carrier (including a lowercase-key variant) before falling back to the system property and _X_AMZN_TRACE_ID, while preserving the existing behavior where the request X-Amzn-Trace-Id can still be extracted for span-linking when an active parent is already present.

Changes:

• Prefer reading com.amazonaws.xray.traceHeader from the extraction carrier before checking the system property and environment variable.
• Add support for the lowercase carrier key (com.amazonaws.xray.traceheader) to match behavior of certain map-based getters.
• Add/extend unit tests to cover precedence, lowercase-key handling, and span-link behavior.

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	Extract Lambda trace header from the carrier first (with lowercase-key fallback) before system/env fallbacks.
aws-xray-propagator/src/test/java/io/opentelemetry/contrib/awsxray/propagator/AwsXrayLambdaPropagatorTest.java	Adds tests validating carrier precedence, lowercase key support, and link behavior remains intact.

[akg268]

Gentle ping @srprash @wangzlei when you have a chance. The checks are green and Copilot did not report any comments. This is the contrib-side companion for open-telemetry/opentelemetry-java-instrumentation#19438 to support Lambda X-Ray trace-header priority.