feat: Enhance agent snapshot serialization with error handling for non-serializable inputs

haystack/core/pipeline/breakpoint.py

@@ -375,13 +375,32 @@ def _create_agent_snapshot(
     :param agent_breakpoint: AgentBreakpoint object containing breakpoints
     :return: An AgentSnapshot containing the agent's state and component visits.
     """
+    try:
+        serialized_chat_generator = _serialize_value_with_schema(
+            _deepcopy_with_exceptions(component_inputs["chat_generator"])
+        )
+    except Exception as error:
+        logger.warning(
+            "Failed to serialize the agent's chat_generator inputs. "
+            "The inputs in the snapshot will be replaced with an empty dictionary. Error: {e}",
+            e=error,
+        )
+        serialized_chat_generator = {}
+
+    try:
+        serialized_tool_invoker = _serialize_value_with_schema(
+            _deepcopy_with_exceptions(component_inputs["tool_invoker"])
+        )
+    except Exception as error:
+        logger.warning(
+            "Failed to serialize the agent's tool_invoker inputs. "
+            "The inputs in the snapshot will be replaced with an empty dictionary. Error: {e}",
+            e=error,
+        )
+        serialized_tool_invoker = {}
+
     return AgentSnapshot(
-        component_inputs={
-            "chat_generator": _serialize_value_with_schema(
-                _deepcopy_with_exceptions(component_inputs["chat_generator"])
-            ),
-            "tool_invoker": _serialize_value_with_schema(_deepcopy_with_exceptions(component_inputs["tool_invoker"])),
-        },
+        component_inputs={"chat_generator": serialized_chat_generator, "tool_invoker": serialized_tool_invoker},
         component_visits=component_visits,
         break_point=agent_breakpoint,
         timestamp=datetime.now(),

releasenotes/notes/error-handling-agent-snapshot-bd5adfd458e9981a.yaml

@@ -0,0 +1,7 @@
+---
+enhancements:
+  - |
+    Made ``_create_agent_snapshot`` robust towards serialization errors. If serializing
+    agent component inputs fails, a warning is logged and an empty dictionary is used
+    as a fallback, preventing the serialization error from masking the real pipeline
+    runtime error.

test/core/pipeline/test_breakpoint.py

@@ -12,14 +12,15 @@
 from haystack.core.pipeline import Pipeline
 from haystack.core.pipeline.breakpoint import (
     HAYSTACK_PIPELINE_SNAPSHOT_SAVE_ENABLED,
+    _create_agent_snapshot,
     _create_pipeline_snapshot,
     _is_snapshot_save_enabled,
     _save_pipeline_snapshot,
     _transform_json_structure,
     load_pipeline_snapshot,
 )
 from haystack.dataclasses import ChatMessage
-from haystack.dataclasses.breakpoints import Breakpoint, PipelineSnapshot, PipelineState
+from haystack.dataclasses.breakpoints import AgentBreakpoint, Breakpoint, PipelineSnapshot, PipelineState
 
 
 def test_transform_json_structure_unwraps_sender_value():
@@ -239,6 +240,74 @@ def to_dict(self):
         assert any("Failed to serialize original input data for `pipeline.run`." in msg for msg in caplog.messages)
 
 
+class TestCreateAgentSnapshot:
+    def test_create_agent_snapshot_non_serializable_chat_generator(self, caplog):
+        class NonSerializable:
+            def to_dict(self):
+                raise TypeError("Cannot serialize")
+
+        agent_breakpoint = AgentBreakpoint(
+            agent_name="agent", break_point=Breakpoint(component_name="chat_generator", visit_count=1)
+        )
+
+        with caplog.at_level(logging.WARNING):
+            snapshot = _create_agent_snapshot(
+                component_visits={"chat_generator": 1, "tool_invoker": 0},
+                agent_breakpoint=agent_breakpoint,
+                component_inputs={"chat_generator": {"messages": NonSerializable()}, "tool_invoker": {"messages": []}},
+            )
+
+        assert snapshot.component_inputs["chat_generator"] == {}
+        assert snapshot.component_inputs["tool_invoker"] != {}
+        assert "Failed to serialize the agent's chat_generator inputs" in caplog.text
+
+    def test_create_agent_snapshot_non_serializable_tool_invoker(self, caplog):
+        class NonSerializable:
+            def to_dict(self):
+                raise TypeError("Cannot serialize")
+
+        agent_breakpoint = AgentBreakpoint(
+            agent_name="agent", break_point=Breakpoint(component_name="chat_generator", visit_count=1)
+        )
+
+        with caplog.at_level(logging.WARNING):
+            snapshot = _create_agent_snapshot(
+                component_visits={"chat_generator": 1, "tool_invoker": 0},
+                agent_breakpoint=agent_breakpoint,
+                component_inputs={"chat_generator": {"messages": []}, "tool_invoker": {"messages": NonSerializable()}},
+            )
+
+        assert snapshot.component_inputs["tool_invoker"] == {}
+        assert snapshot.component_inputs["chat_generator"] != {}
+        assert "Failed to serialize the agent's tool_invoker inputs" in caplog.text
+
+    def test_create_agent_snapshot_both_non_serializable(self, caplog):
+        class NonSerializable:
+            def to_dict(self):
+                raise TypeError("Cannot serialize")
+
+        agent_breakpoint = AgentBreakpoint(
+            agent_name="agent", break_point=Breakpoint(component_name="chat_generator", visit_count=1)
+        )
+
+        with caplog.at_level(logging.WARNING):
+            snapshot = _create_agent_snapshot(
+                component_visits={"chat_generator": 1, "tool_invoker": 0},
+                agent_breakpoint=agent_breakpoint,
+                component_inputs={
+                    "chat_generator": {"messages": NonSerializable()},
+                    "tool_invoker": {"messages": NonSerializable()},
+                },
+            )
+
+        assert snapshot.component_inputs["chat_generator"] == {}
+        assert snapshot.component_inputs["tool_invoker"] == {}
+        assert "Failed to serialize the agent's chat_generator inputs" in caplog.text
+        assert "Failed to serialize the agent's tool_invoker inputs" in caplog.text
+        assert snapshot.component_visits == {"chat_generator": 1, "tool_invoker": 0}
+        assert snapshot.break_point == agent_breakpoint
+
+
 def test_save_pipeline_snapshot_raises_on_failure(tmp_path, caplog, monkeypatch):
     monkeypatch.setenv(HAYSTACK_PIPELINE_SNAPSHOT_SAVE_ENABLED, "true")