[Core] Fix traceparent header in DistributedTracingPolicy

[pvaneck]

When we get the trace context headers, we should first ensure that we are inside the HTTP span's context to ensure that the traceparent header corresponds to the HTTP span's context.

[azure-sdk]

API change check

API changes are not detected in this pull request.

Pull Request Overview

This PR fixes the traceparent header generation in the DistributedTracingPolicy so that the header reflects the HTTP span context correctly. Key changes include updating tests to verify the new header format, modifying the tracing_common header logic, and adjusting the distributed tracing policy to use the proper context manager.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
sdk/core/azure-core/tests/test_tracing_policy.py	Updated test assertions to check the new traceparent header format and added assertions to validate span IDs with OpenTelemetry formatting.
sdk/core/azure-core/tests/tracing_common.py	Changed the span_instance method implementation by removing the _span attribute and using self instead, and adjusted context management accordingly.
sdk/core/azure-core/azure/core/pipeline/policies/_distributed_tracing.py	Updated request handling with the new change_context pattern and modified the assignment of the tracing context.
sdk/core/azure-core/CHANGELOG.md	Updated changelog to document the fix in the traceparent header.
sdk/core/azure-core/azure/core/tracing/opentelemetry.py	Refined type hints for suppression-related methods.

Comments suppressed due to low confidence (3)

sdk/core/azure-core/tests/tracing_common.py:37

• Removing the assignment to self._span and switching to returning self in span_instance may affect code that relies on the previous behavior. Please verify that this change is intentional and update any related documentation or usage accordingly.

self._span = span

sdk/core/azure-core/azure/core/pipeline/policies/_distributed_tracing.py:160

• There appears to be a duplicate assignment of otel_span to request.context[self.TRACING_CONTEXT]. Consider removing the redundant assignment for clarity and to avoid potential side-effects.

request.context[self.TRACING_CONTEXT] = otel_span

sdk/core/azure-core/tests/test_tracing_policy.py:386

• The variable 'traceparent' is used without being defined in this test context. Please ensure that 'traceparent' is retrieved from the correct source, such as the request headers, before splitting its value.

assert traceparent.split("-")[1] == format_trace_id(span_context.trace_id)