docs(langchain): document trace continuity and parent span requirement for bare agent loops (#4347)

[ArjunPakhan]

Problem

When executing a bare LangChain agent loop (e.g., repeatedly invoking model.invoke and tool executions without an enclosing parent span or @workflow decorator), each callback root initiates a separate trace ID. This results in parentless, fragmented spans across a single logical task, making cross-span reasoning and trace replay difficult downstream (#4347).

Solution

Added a Trace Continuity in Agent Loops section to the LangChain instrumentation documentation (packages/opentelemetry-instrumentation-langchain/README.md).

The new section explicitly documents:

1. Why bare loops produce independent trace IDs per invocation.
2. How to wrap execution loops in a parent span or apply the @workflow decorator to ensure all steps within an agent loop share a single trace context.

Related Issue

Fixes #4347

Checklist

• Documentation has been updated cleanly.
• Scope is isolated strictly to issue LangChain: bare tool loop without a workflow span produces one trace per invocation — expected? docs note? #4347.

Summary by CodeRabbit

• Documentation
  • Added traceloop-sdk to the installation instructions.
  • Added guidance for maintaining trace continuity in bare LangChain agent loops.
  • Included examples using a parent span or the @workflow decorator to preserve a shared trace.

[CLAassistant]

All committers have signed the CLA.

[coderabbitai]

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📝 Walkthrough

Walkthrough

The LangChain instrumentation README now documents separate root traces for bare agent loops, shows how a parent span or @workflow preserves trace continuity, and adds traceloop-sdk to installation instructions.

Changes

LangChain trace continuity

Layer / File(s)	Summary
Trace continuity guidance packages/opentelemetry-instrumentation-langchain/README.md	The README adds traceloop-sdk to the installation command. It explains separate root spans for standalone model and tool calls. It adds a @workflow example that wraps the agent loop in a parent span.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Merge Risk: ⚪ Minimal · up to 742f1

This is a localized documentation-only change describing trace continuity for bare agent loops, with no actionable merge-blocking risk remaining after normal checks and review.

Possibly related PRs

• traceloop/openllmetry#4395: Fixes context scoping for @workflow and @agent spans, which relates to the documented trace-continuity behavior.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the documentation change for trace continuity and parent spans in bare LangChain agent loops.
Linked Issues check	✅ Passed	The README documents the trace fragmentation behavior and the parent span or @workflow solutions requested by issue #4347.
Out of Scope Changes check	✅ Passed	All changes support the linked issue by documenting trace continuity and updating installation instructions for the workflow example.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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• Create PR with unit tests

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Actionable comments posted: 1

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Inline comments:
In `@packages/opentelemetry-instrumentation-langchain/README.md`:
- Line 30: Update the installation instructions in the README example to include
the traceloop-sdk package alongside opentelemetry-instrumentation-langchain,
since the example imports workflow from traceloop.sdk.decorators.

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Reviewing files that changed from the base of the PR and between 62e24c2 and 9a5eb8a.

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• packages/opentelemetry-instrumentation-langchain/README.md

Included review availability: Your plan includes up to 8 reviews per rolling hour; 7 remain after this review.