feat(tracing): add optional Langfuse support (#1717)

* feat(tracing): add optional Langfuse support

* Fix tracing fail-fast behavior for explicitly enabled providers

* fix(lint)

backend/tests/test_tracing_config.py

@@ -2,6 +2,8 @@
 
 from __future__ import annotations
 
+import pytest
+
 from deerflow.config import tracing_config as tracing_module
 
 
@@ -9,6 +11,29 @@ def _reset_tracing_cache() -> None:
     tracing_module._tracing_config = None
 
 
+@pytest.fixture(autouse=True)
+def clear_tracing_env(monkeypatch):
+    for name in (
+        "LANGSMITH_TRACING",
+        "LANGCHAIN_TRACING_V2",
+        "LANGCHAIN_TRACING",
+        "LANGSMITH_API_KEY",
+        "LANGCHAIN_API_KEY",
+        "LANGSMITH_PROJECT",
+        "LANGCHAIN_PROJECT",
+        "LANGSMITH_ENDPOINT",
+        "LANGCHAIN_ENDPOINT",
+        "LANGFUSE_TRACING",
+        "LANGFUSE_PUBLIC_KEY",
+        "LANGFUSE_SECRET_KEY",
+        "LANGFUSE_BASE_URL",
+    ):
+        monkeypatch.delenv(name, raising=False)
+    _reset_tracing_cache()
+    yield
+    _reset_tracing_cache()
+
+
 def test_prefers_langsmith_env_names(monkeypatch):
     monkeypatch.setenv("LANGSMITH_TRACING", "true")
     monkeypatch.setenv("LANGSMITH_API_KEY", "lsv2_key")
@@ -18,11 +43,12 @@ def test_prefers_langsmith_env_names(monkeypatch):
     _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 cfg.langsmith.enabled is True
+    assert cfg.langsmith.api_key == "lsv2_key"
+    assert cfg.langsmith.project == "smith-project"
+    assert cfg.langsmith.endpoint == "https://smith.example.com"
     assert tracing_module.is_tracing_enabled() is True
+    assert tracing_module.get_enabled_tracing_providers() == ["langsmith"]
 
 
 def test_falls_back_to_langchain_env_names(monkeypatch):
@@ -39,11 +65,12 @@ def test_falls_back_to_langchain_env_names(monkeypatch):
     _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 cfg.langsmith.enabled is True
+    assert cfg.langsmith.api_key == "legacy-key"
+    assert cfg.langsmith.project == "legacy-project"
+    assert cfg.langsmith.endpoint == "https://legacy.example.com"
     assert tracing_module.is_tracing_enabled() is True
+    assert tracing_module.get_enabled_tracing_providers() == ["langsmith"]
 
 
 def test_langsmith_tracing_false_overrides_langchain_tracing_v2_true(monkeypatch):
@@ -55,8 +82,9 @@ def test_langsmith_tracing_false_overrides_langchain_tracing_v2_true(monkeypatch
     _reset_tracing_cache()
     cfg = tracing_module.get_tracing_config()
 
-    assert cfg.enabled is False
+    assert cfg.langsmith.enabled is False
     assert tracing_module.is_tracing_enabled() is False
+    assert tracing_module.get_enabled_tracing_providers() == []
 
 
 def test_defaults_when_project_not_set(monkeypatch):
@@ -68,4 +96,51 @@ def test_defaults_when_project_not_set(monkeypatch):
     _reset_tracing_cache()
     cfg = tracing_module.get_tracing_config()
 
-    assert cfg.project == "deer-flow"
+    assert cfg.langsmith.project == "deer-flow"
+
+
+def test_langfuse_config_is_loaded(monkeypatch):
+    monkeypatch.setenv("LANGFUSE_TRACING", "true")
+    monkeypatch.setenv("LANGFUSE_PUBLIC_KEY", "pk-lf-test")
+    monkeypatch.setenv("LANGFUSE_SECRET_KEY", "sk-lf-test")
+    monkeypatch.setenv("LANGFUSE_BASE_URL", "https://langfuse.example.com")
+
+    _reset_tracing_cache()
+    cfg = tracing_module.get_tracing_config()
+
+    assert cfg.langfuse.enabled is True
+    assert cfg.langfuse.public_key == "pk-lf-test"
+    assert cfg.langfuse.secret_key == "sk-lf-test"
+    assert cfg.langfuse.host == "https://langfuse.example.com"
+    assert tracing_module.get_enabled_tracing_providers() == ["langfuse"]
+
+
+def test_dual_provider_config_is_loaded(monkeypatch):
+    monkeypatch.setenv("LANGSMITH_TRACING", "true")
+    monkeypatch.setenv("LANGSMITH_API_KEY", "lsv2_key")
+    monkeypatch.setenv("LANGFUSE_TRACING", "true")
+    monkeypatch.setenv("LANGFUSE_PUBLIC_KEY", "pk-lf-test")
+    monkeypatch.setenv("LANGFUSE_SECRET_KEY", "sk-lf-test")
+
+    _reset_tracing_cache()
+    cfg = tracing_module.get_tracing_config()
+
+    assert cfg.langsmith.is_configured is True
+    assert cfg.langfuse.is_configured is True
+    assert tracing_module.is_tracing_enabled() is True
+    assert tracing_module.get_enabled_tracing_providers() == ["langsmith", "langfuse"]
+
+
+def test_langfuse_enabled_requires_public_and_secret_keys(monkeypatch):
+    monkeypatch.setenv("LANGFUSE_TRACING", "true")
+    monkeypatch.delenv("LANGFUSE_PUBLIC_KEY", raising=False)
+    monkeypatch.setenv("LANGFUSE_SECRET_KEY", "sk-lf-test")
+
+    _reset_tracing_cache()
+
+    assert tracing_module.get_tracing_config().is_configured is False
+    assert tracing_module.get_enabled_tracing_providers() == []
+    assert tracing_module.get_tracing_config().explicitly_enabled_providers == ["langfuse"]
+
+    with pytest.raises(ValueError, match="LANGFUSE_PUBLIC_KEY"):
+        tracing_module.validate_enabled_tracing_providers()