fix(tracing): support LANGCHAIN_* env fallback for LangSmith config

- add backward-compatible env parsing in tracing_config.py
- support fallback keys:
   LANGCHAIN_TRACING_V2 / LANGCHAIN_TRACING
   LANGCHAIN_API_KEY
   LANGCHAIN_PROJECT
   LANGCHAIN_ENDPOINT
- keep LANGSMITH_* as preferred source when both are present
- add regression tests in test_tracing_config.py

Author: WillemJiang

backend/src/config/tracing_config.py

@@ -25,6 +25,25 @@ def is_configured(self) -> bool:
 _tracing_config: TracingConfig | None = None
 
 
+def _env_flag_true(*names: str) -> bool:
+    """Return True when any provided env var is set to a truthy value."""
+    truthy_values = {"1", "true", "yes", "on"}
+    for name in names:
+        value = os.environ.get(name)
+        if value and value.strip().lower() in truthy_values:
+            return True
+    return False
+
+
+def _first_env_value(*names: str) -> str | None:
+    """Return the first non-empty environment value from candidate names."""
+    for name in names:
+        value = os.environ.get(name)
+        if value and value.strip():
+            return value.strip()
+    return None
+
+
 def get_tracing_config() -> TracingConfig:
     """Get the current tracing configuration from environment variables.
     Returns:
@@ -37,10 +56,11 @@ def get_tracing_config() -> TracingConfig:
         if _tracing_config is not None:  # Double-check after acquiring lock
             return _tracing_config
         _tracing_config = TracingConfig(
-            enabled=os.environ.get("LANGSMITH_TRACING", "").lower() == "true",
-            api_key=os.environ.get("LANGSMITH_API_KEY"),
-            project=os.environ.get("LANGSMITH_PROJECT", "deer-flow"),
-            endpoint=os.environ.get("LANGSMITH_ENDPOINT", "https://api.smith.langchain.com"),
+            # Keep compatibility with both legacy LANGCHAIN_* and newer LANGSMITH_* variables.
+            enabled=_env_flag_true("LANGSMITH_TRACING", "LANGCHAIN_TRACING_V2", "LANGCHAIN_TRACING"),
+            api_key=_first_env_value("LANGSMITH_API_KEY", "LANGCHAIN_API_KEY"),
+            project=_first_env_value("LANGSMITH_PROJECT", "LANGCHAIN_PROJECT") or "deer-flow",
+            endpoint=_first_env_value("LANGSMITH_ENDPOINT", "LANGCHAIN_ENDPOINT") or "https://api.smith.langchain.com",
         )
         return _tracing_config
 

backend/tests/test_tracing_config.py

@@ -0,0 +1,58 @@
+"""Tests for src.config.tracing_config."""
+
+from __future__ import annotations
+
+from src.config import tracing_config as tracing_module
+
+
+def _reset_tracing_cache() -> None:
+    tracing_module._tracing_config = None
+
+
+def test_prefers_langsmith_env_names(monkeypatch):
+    monkeypatch.setenv("LANGSMITH_TRACING", "true")
+    monkeypatch.setenv("LANGSMITH_API_KEY", "lsv2_key")
+    monkeypatch.setenv("LANGSMITH_PROJECT", "smith-project")
+    monkeypatch.setenv("LANGSMITH_ENDPOINT", "https://smith.example.com")
+
+    _reset_tracing_cache()
+    cfg = tracing_module.get_tracing_config()
+
+    assert cfg.enabled is True
+    assert cfg.api_key == "lsv2_key"
+    assert cfg.project == "smith-project"
+    assert cfg.endpoint == "https://smith.example.com"
+    assert tracing_module.is_tracing_enabled() is True
+
+
+def test_falls_back_to_langchain_env_names(monkeypatch):
+    monkeypatch.delenv("LANGSMITH_TRACING", raising=False)
+    monkeypatch.delenv("LANGSMITH_API_KEY", raising=False)
+    monkeypatch.delenv("LANGSMITH_PROJECT", raising=False)
+    monkeypatch.delenv("LANGSMITH_ENDPOINT", raising=False)
+
+    monkeypatch.setenv("LANGCHAIN_TRACING_V2", "true")
+    monkeypatch.setenv("LANGCHAIN_API_KEY", "legacy-key")
+    monkeypatch.setenv("LANGCHAIN_PROJECT", "legacy-project")
+    monkeypatch.setenv("LANGCHAIN_ENDPOINT", "https://legacy.example.com")
+
+    _reset_tracing_cache()
+    cfg = tracing_module.get_tracing_config()
+
+    assert cfg.enabled is True
+    assert cfg.api_key == "legacy-key"
+    assert cfg.project == "legacy-project"
+    assert cfg.endpoint == "https://legacy.example.com"
+    assert tracing_module.is_tracing_enabled() is True
+
+
+def test_defaults_when_project_not_set(monkeypatch):
+    monkeypatch.setenv("LANGSMITH_TRACING", "yes")
+    monkeypatch.setenv("LANGSMITH_API_KEY", "key")
+    monkeypatch.delenv("LANGSMITH_PROJECT", raising=False)
+    monkeypatch.delenv("LANGCHAIN_PROJECT", raising=False)
+
+    _reset_tracing_cache()
+    cfg = tracing_module.get_tracing_config()
+
+    assert cfg.project == "deer-flow"