From 5e579e3b0d547bfa353f6b3d1ed6dc653c468c69 Mon Sep 17 00:00:00 2001
From: gjija <agonavdimetaj@gmail.com>
Date: Tue, 10 Nov 2026 00:02:02 +0000
Subject: [PATCH] fix(agents): read LangGraphAgent reply text from content
 blocks

LangGraphAgent passed the last message's `content` straight to
`Part.from_text`. LangChain message content can be a list of content
blocks, for example a reasoning block and a text block. `Part.from_text`
then fails pydantic validation and the agent raises instead of answering.

When the content is a list, use the message's `.text` property, which
keeps only the text. String content is passed through unchanged, so
installs still on langchain-core 0.3, where `.text` is a method, keep
working.
---
 src/google/adk/agents/langgraph_agent.py      |  7 +++-
 .../unittests/agents/test_langgraph_agent.py  | 34 +++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/src/google/adk/agents/langgraph_agent.py b/src/google/adk/agents/langgraph_agent.py
index f1dd1ed8775..875cdf48d8a 100644
--- a/src/google/adk/agents/langgraph_agent.py
+++ b/src/google/adk/agents/langgraph_agent.py
@@ -140,7 +140,12 @@ async def _run_async_impl(
 
     # Use the Runnable
     final_state = await self.graph.ainvoke({'messages': messages}, config)
-    result = final_state['messages'][-1].content
+    message = final_state['messages'][-1]
+    # Content can be a list of blocks (e.g. reasoning and text); `.text` keeps
+    # only the text. String content is passed through unchanged.
+    result = (
+        message.content if isinstance(message.content, str) else message.text
+    )
 
     result_event = Event(
         invocation_id=ctx.invocation_id,
diff --git a/tests/unittests/agents/test_langgraph_agent.py b/tests/unittests/agents/test_langgraph_agent.py
index e7b73a7b253..514919f0cae 100644
--- a/tests/unittests/agents/test_langgraph_agent.py
+++ b/tests/unittests/agents/test_langgraph_agent.py
@@ -261,6 +261,40 @@ def respond(state: MessagesState) -> dict[str, list[AIMessage]]:
   assert observed_messages[0].content == "test system prompt"
 
 
+@pytest.mark.asyncio
+async def test_langgraph_agent_reads_text_from_content_blocks():
+  """A reply whose content is a list of blocks yields its text."""
+
+  def respond(state: MessagesState) -> dict[str, list[AIMessage]]:
+    del state
+    return {
+        "messages": [
+            AIMessage(
+                content=[
+                    {"type": "reasoning", "reasoning": "thinking"},
+                    {"type": "text", "text": "Sunny today."},
+                ]
+            )
+        ]
+    }
+
+  graph_builder = StateGraph(MessagesState)
+  graph_builder.add_node("respond", respond)
+  graph_builder.set_entry_point("respond")
+  graph_builder.set_finish_point("respond")
+  agent = LangGraphAgent(name="weather_agent", graph=graph_builder.compile())
+
+  events = [
+      event
+      async for event in agent.run_async(
+          _make_parent_context("test_app", "test_user", "session-id")
+      )
+  ]
+
+  assert len(events) == 1
+  assert events[0].content.parts[0].text == "Sunny today."
+
+
 def test_get_thread_id_is_stable_across_processes():
   """A literal digest also rejects a swap to a per-process-salted hash."""
   assert (