fix(llmobs): propagate llmobs_parent_id in _current_trace_context

[jasonmp85]

Summary

_current_trace_context() sets PROPAGATED_LLMOBS_TRACE_ID_KEY (_dd.p.llmobs_trace_id) on the returned context but omits PROPAGATED_PARENT_ID_KEY (_dd.p.llmobs_parent_id). Any consumer that reads context._meta directly — including HTTPPropagator.inject and non-Python clients (Go, Java, etc.) receiving the propagated headers — will see the trace ID but not the parent span ID.

This breaks distributed LLMObs tracing to non-Python services. For example, dd-trace-go's contextWithPropagatedLLMSpan requires both tags to be non-empty before it attaches the propagated LLMObs context:

if propagatedLLMObs.SpanID == "" || propagatedLLMObs.TraceID == "" {
    // falls through to newLLMObsTraceID() — starts a fresh, unrelated trace
}

Without _dd.p.llmobs_parent_id, a downstream Go service starts a new root LLMObs trace instead of inheriting the parent, breaking the distributed trace tree.

Fix

One line in _current_trace_context():

context._meta[PROPAGATED_PARENT_ID_KEY] = str(active.span_id)

PROPAGATED_PARENT_ID_KEY is already defined in _constants.py and imported in _llmobs.py — it was just never set on this code path.

Note: _inject_llmobs_context (the http.span_inject path, used by inject_distributed_headers) already sets this correctly. This fix brings _current_trace_context to parity.

Test

Added test_current_trace_context_includes_parent_id to tests/llmobs/test_propagation.py. Asserts that the context returned by _current_trace_context() has both PROPAGATED_PARENT_ID_KEY and PROPAGATED_LLMOBS_TRACE_ID_KEY set, with parent_id == str(span.span_id).

[cit-pr-commenter-54b7da]

Codeowners resolved as

releasenotes/notes/llmobs-propagate-parent-id-401cc2c7a9274277.yaml     @DataDog/apm-python

[datadog-prod-us1-3]

 

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