langchain: gen_ai.conversation.id is set only on invoke_agent spans #475

Describe your environment

OS: Ubuntu 22.04
Python version: Python 3.12
Package version: opentelemetry-instrumentation-genai-langchain 1.1b1, opentelemetry-util-genai 1.1b0 (also reproduces on main)
GenAI library (e.g. anthropic, openai) and version: langchain 1.3.16, langchain-openai 1.4.3

What happened?

The LangChain instrumentation reads a conversation identifier from the
thread_id, session_id, or conversation_id metadata keys, but only applies
it to invoke_agent spans. The chat and invoke_workflow spans in the same
trace have no gen_ai.conversation.id, even though semconv defines the
attribute as conditionally required on all three.
WorkflowInvocation in opentelemetry-util-genai has no conversation_id
field at all, so an invoke_workflow span cannot carry one even when the
application supplies it.
Separately, AgentInvocation applies the attribute from
_get_request_attributes, which runs when the span finishes. The attribute is
absent for the whole life of the span, so a SpanProcessor.on_start cannot see
it and a child span cannot read it from its parent.

Steps to Reproduce

examples/agent/main.py in the langchain package already reproduces this — it
sets session_id in the agent's metadata:

agent = create_react_agent(llm, tools=[multiply, add]).with_config(
    {
        "metadata": {
            "agent_name": "coordinator",
            "session_id": session_id,
        },
    }
)

Run it against any exporter and inspect the resulting spans, or swap the OTLP
exporters for an InMemorySpanExporter and print gen_ai.conversation.id for
each span.

Expected Result

Every span in the trace that semconv defines the attribute for carries it — the
invoke_agent span, the chat spans for the model calls it makes, and the
invoke_workflow span if the run is classified as a workflow.

Actual Result

Only the invoke_agent span carries gen_ai.conversation.id. The chat spans
and any invoke_workflow span have no such attribute.

Additional context

No response

Would you like to implement a fix?

Yes

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