Core[major]: Base Tracer to propagate raw output from tool for on_tool_end (#18932)

This PR completes work for PR #18798 to expose raw tool output in
on_tool_end.

Affected APIs:
* astream_log
* astream_events
* callbacks sent to langsmith via langsmith-sdk
* Any other code that relies on BaseTracer!

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>
Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/core/langchain_core/callbacks/manager.py

@@ -984,7 +984,6 @@ class CallbackManagerForToolRun(ParentRunManager, ToolManagerMixin):
         Args:
             output (Any): The output of the tool.
         """
-        output = str(output)
         handle_event(
             self.handlers,
             "on_tool_end",

libs/core/langchain_core/tracers/base.py

@@ -506,7 +506,6 @@ class BaseTracer(BaseCallbackHandler, ABC):
 
     def on_tool_end(self, output: Any, *, run_id: UUID, **kwargs: Any) -> Run:
         """End a trace for a tool run."""
-        output = str(output)
         tool_run = self._get_run(run_id, run_type="tool")
         tool_run.outputs = {"output": output}
         tool_run.end_time = datetime.now(timezone.utc)

libs/core/tests/unit_tests/runnables/test_runnable_events.py

@@ -52,6 +52,88 @@ async def _collect_events(events: AsyncIterator[StreamEvent]) -> List[StreamEven
     return events_
 
 
+async def test_event_stream_with_simple_function_tool() -> None:
+    """Test the event stream with a function and tool"""
+
+    def foo(x: int) -> dict:
+        """Foo"""
+        return {"x": 5}
+
+    @tool
+    def get_docs(x: int) -> List[Document]:
+        """Hello Doc"""
+        return [Document(page_content="hello")]
+
+    chain = RunnableLambda(foo) | get_docs
+    events = await _collect_events(chain.astream_events({}, version="v1"))
+    assert events == [
+        {
+            "event": "on_chain_start",
+            "run_id": "",
+            "name": "RunnableSequence",
+            "tags": [],
+            "metadata": {},
+            "data": {"input": {}},
+        },
+        {
+            "event": "on_chain_start",
+            "name": "foo",
+            "run_id": "",
+            "tags": ["seq:step:1"],
+            "metadata": {},
+            "data": {},
+        },
+        {
+            "event": "on_chain_stream",
+            "name": "foo",
+            "run_id": "",
+            "tags": ["seq:step:1"],
+            "metadata": {},
+            "data": {"chunk": {"x": 5}},
+        },
+        {
+            "event": "on_chain_end",
+            "name": "foo",
+            "run_id": "",
+            "tags": ["seq:step:1"],
+            "metadata": {},
+            "data": {"input": {}, "output": {"x": 5}},
+        },
+        {
+            "event": "on_tool_start",
+            "name": "get_docs",
+            "run_id": "",
+            "tags": ["seq:step:2"],
+            "metadata": {},
+            "data": {"input": {"x": 5}},
+        },
+        {
+            "event": "on_tool_end",
+            "name": "get_docs",
+            "run_id": "",
+            "tags": ["seq:step:2"],
+            "metadata": {},
+            "data": {"input": {"x": 5}, "output": [Document(page_content="hello")]},
+        },
+        {
+            "event": "on_chain_stream",
+            "run_id": "",
+            "tags": [],
+            "metadata": {},
+            "name": "RunnableSequence",
+            "data": {"chunk": [Document(page_content="hello")]},
+        },
+        {
+            "event": "on_chain_end",
+            "name": "RunnableSequence",
+            "run_id": "",
+            "tags": [],
+            "metadata": {},
+            "data": {"output": [Document(page_content="hello")]},
+        },
+    ]
+
+
 async def test_event_stream_with_single_lambda() -> None:
     """Test the event stream with a tool."""