From 99fd32a8eb74b9fc31eb140c6117d4650440ed8d Mon Sep 17 00:00:00 2001
From: poshinchen <pschen@amazon.com>
Date: Wed, 15 Jul 2026 15:22:38 -0400
Subject: [PATCH] fix: convert Langfuse AGENT observations regardless of parent

Strands SDK traces nest the AGENT observation under a framework SPAN, so
the null-parent gate on the combined CHAIN/AGENT branch dropped every
Strands agent invocation. No AgentInvocationSpan was produced, and every
evaluator calling _get_last_turn() failed with ValueError.

Route AGENT to _convert_agent_invocation unconditionally; keep the
null-parent check on CHAIN, where only the root chain is the agent
invocation (LangChain emits a CHAIN per sub-chain).

Fixes #311
---
 .../providers/langfuse_provider.py            | 13 ++++-
 .../providers/test_langfuse_provider.py       | 53 +++++++++++++++++++
 2 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/src/strands_evals/providers/langfuse_provider.py b/src/strands_evals/providers/langfuse_provider.py
index 3504a2b9..75870682 100644
--- a/src/strands_evals/providers/langfuse_provider.py
+++ b/src/strands_evals/providers/langfuse_provider.py
@@ -206,11 +206,17 @@ def _convert_observation(self, obs: Any, session_id: str) -> Any:
         Routing:
             obs.type == "GENERATION"                        → InferenceSpan
             obs.type == "TOOL"                              → ToolExecutionSpan
+            obs.type == "AGENT"                             → AgentInvocationSpan (Langfuse v4+)
             obs.type == "CHAIN" and no parent               → AgentInvocationSpan
-            obs.type == "AGENT" and no parent               → AgentInvocationSpan (Langfuse v4+)
             obs.type == "SPAN", name starts "execute_tool"  → ToolExecutionSpan
             obs.type == "SPAN", name starts "invoke_agent"  → AgentInvocationSpan
             Otherwise                                       → None (skipped)
+
+        Note: AGENT observations are converted regardless of parent. Strands SDK
+        traces nest the AGENT observation under a framework SPAN, so requiring a
+        null parent (as CHAIN does) would drop every Strands agent invocation.
+        CHAIN keeps the null-parent check because LangChain emits a CHAIN per
+        sub-chain and only the root chain is the agent invocation.
         """
         obs_type = obs.type
 
@@ -220,7 +226,10 @@ def _convert_observation(self, obs: Any, session_id: str) -> Any:
         if obs_type == "TOOL":
             return self._convert_tool_execution(obs, session_id)
 
-        if obs_type in ("CHAIN", "AGENT") and obs.parent_observation_id is None:
+        if obs_type == "AGENT":
+            return self._convert_agent_invocation(obs, session_id)
+
+        if obs_type == "CHAIN" and obs.parent_observation_id is None:
             return self._convert_agent_invocation(obs, session_id)
 
         # Strands-specific fallback for SPAN type
diff --git a/tests/strands_evals/providers/test_langfuse_provider.py b/tests/strands_evals/providers/test_langfuse_provider.py
index 7b74a2c7..4666707a 100644
--- a/tests/strands_evals/providers/test_langfuse_provider.py
+++ b/tests/strands_evals/providers/test_langfuse_provider.py
@@ -872,6 +872,59 @@ def test_chain_with_content_output(self, provider, mock_client):
         assert agents[0].agent_response == "Hello!"
 
 
+class TestLangfuseAgentType:
+    """AGENT-type observations (Langfuse v4+ / Strands via OTEL)."""
+
+    def _get_spans(self, provider, mock_client, observations):
+        mock_client.api.trace.list.return_value = _paginated([_trace("t1", "s1")])
+        mock_client.api.observations.get_many.return_value = _paginated(observations)
+        return provider.get_evaluation_data("s1")["trajectory"].traces[0].spans
+
+    def test_agent_with_parent_produces_agent_invocation(self, provider, mock_client):
+        """AGENT nested under a SPAN parent → AgentInvocationSpan (issue #311)."""
+        spans = self._get_spans(
+            provider,
+            mock_client,
+            [
+                _obs(
+                    "o-agent",
+                    "t1",
+                    "AGENT",
+                    name="invoke_agent Strands Agents",
+                    obs_input="What is 2+2?",
+                    obs_output="4",
+                    parent_observation_id="o-span",
+                ),
+            ],
+        )
+        agents = [s for s in spans if isinstance(s, AgentInvocationSpan)]
+        assert len(agents) == 1
+        assert agents[0].user_prompt == "What is 2+2?"
+        assert agents[0].agent_response == "4"
+
+    def test_root_agent_produces_agent_invocation(self, provider, mock_client):
+        """AGENT at the root (no parent) → AgentInvocationSpan."""
+        spans = self._get_spans(
+            provider,
+            mock_client,
+            [
+                _obs(
+                    "o-agent",
+                    "t1",
+                    "AGENT",
+                    name="invoke_agent Strands Agents",
+                    obs_input="Hello",
+                    obs_output="Hi!",
+                    parent_observation_id=None,
+                ),
+            ],
+        )
+        agents = [s for s in spans if isinstance(s, AgentInvocationSpan)]
+        assert len(agents) == 1
+        assert agents[0].user_prompt == "Hello"
+        assert agents[0].agent_response == "Hi!"
+
+
 class TestLangChainEndToEnd:
     """Full LangChain agent trace: CHAIN + GENERATION + TOOL."""