feat(langgraph): enable langgraph integration by default (#12977)

LangGraph patching/instrumentation was previously hidden behind a
private environment variable during a beta phase. This PR removes that
gate and enables it by default.

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

---------

Co-authored-by: Yun Kim <[email protected]>

Author: sabrenner

ddtrace/_monkey.py

@@ -52,7 +52,7 @@
     "grpc": True,
     "httpx": True,
     "kafka": True,
-    "langgraph": False,
+    "langgraph": True,
     "litellm": True,
     "mongoengine": True,
     "mysql": True,

ddtrace/contrib/_langgraph.py

@@ -1,4 +1,34 @@
 """
-The LangGraph integration instruments the LangGraph Python library to emit metrics,
-traces, and logs.
+The LangGraph integration instruments the LangGraph Python library to emit traces for
+graph and node invocations.
+
+All traces submitted from the LangGraph integration are tagged by:
+- ``service``, ``env``, ``version``: see the `Unified Service Tagging docs <https://docs.datadoghq.com/getting_started/tagging/unified_service_tagging>`_.
+
+Enabling
+~~~~~~~~
+
+The LangGraph integration is enabled automatically when you use
+:ref:`ddtrace-run<ddtracerun>` or :ref:`import ddtrace.auto<ddtraceauto>`.
+Alternatively, use :func:`patch() <ddtrace.patch>` to manually enable the LangGraph integration::
+    from ddtrace import patch
+    patch(langgraph=True)
+
+Global Configuration
+~~~~~~~~~~~~~~~~~~~~
+
+.. py:data:: ddtrace.config.langgraph["service"]
+   The service name reported by default for LangGraph requests.
+   Alternatively, you can set this option with the ``DD_SERVICE`` or ``DD_LANGGRAPH_SERVICE`` environment
+   variables.
+   Default: ``DD_SERVICE``
+
+Instance Configuration
+~~~~~~~~~~~~~~~~~~~~~~
+
+To configure the LangGraph integration on a per-instance basis use the
+``Pin`` API::
+    import langgraph
+    from ddtrace.trace import Pin
+    Pin.override(langgraph, service="my-langgraph-service")
 """

ddtrace/contrib/internal/langgraph/patch.py

@@ -1,4 +1,3 @@
-import os
 import sys
 
 import langgraph
@@ -208,8 +207,7 @@ def patched_pregel_loop_tick(langgraph, pin, func, instance, args, kwargs):
 
 
 def patch():
-    should_patch = os.getenv("_DD_TRACE_LANGGRAPH_ENABLED", "false").lower() in ("true", "1")
-    if not should_patch or getattr(langgraph, "_datadog_patch", False):
+    if getattr(langgraph, "_datadog_patch", False):
         return
 
     langgraph._datadog_patch = True

releasenotes/notes/enable-langgraph-by-default-917c24b82a2db2ef.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    langgraph: Introduces tracing support for LangGraph, specifically tracing graph and node executions.
+      See `the docs <https://ddtrace.readthedocs.io/en/stable/integrations.html#langgraph>`_
+      for more information.
+  - |
+    LLM Observability: Introduces tracing support for LangGraph graph and node invocation.

tests/contrib/langgraph/conftest.py

@@ -27,7 +27,6 @@ def mock_tracer():
 
 @pytest.fixture
 def langgraph(monkeypatch, mock_tracer):
-    monkeypatch.setenv("_DD_TRACE_LANGGRAPH_ENABLED", "true")
     patch()
     import langgraph
 

tests/contrib/langgraph/test_langgraph_patch.py

@@ -9,9 +9,6 @@
 from tests.utils import call_program
 
 
-os.environ["_DD_TRACE_LANGGRAPH_ENABLED"] = "true"
-
-
 class TestLangGraphPatch(PatchTestCase.Base):
     __integration_name__ = "langgraph"
     __module_name__ = "langgraph"