fix: Fix initializing an Agent from an AgentSnapshot (#9826)

* Fix initializing agent from snapshot. Refactoring tests

* Fixing tests

* Add integration test

* Add reno

* linting

* Update releasenotes/notes/fix-openai-agent-snapshot-init-1ca26789564a53fe.yaml

Co-authored-by: David S. Batista <dsbatista@gmail.com>

---------

Co-authored-by: David S. Batista <dsbatista@gmail.com>

Author: 2 people

haystack/components/agents/agent.py

@@ -359,15 +359,7 @@ def _initialize_from_snapshot(
         state_data = current_inputs["tool_invoker"]["state"].data
         state = State(schema=self.state_schema, data=state_data)
 
-        if isinstance(snapshot.break_point.break_point, ToolBreakpoint):
-            messages = current_inputs["tool_invoker"]["messages"]
-            skip_chat_generator = True
-        else:
-            messages = current_inputs["chat_generator"]["messages"]
-            skip_chat_generator = False
-
-        state.set("messages", messages)
-
+        skip_chat_generator = isinstance(snapshot.break_point.break_point, ToolBreakpoint)
         streaming_callback = current_inputs["chat_generator"].get("streaming_callback", streaming_callback)
         streaming_callback = select_streaming_callback(  # type: ignore[call-overload]
             init_callback=self.streaming_callback, runtime_callback=streaming_callback, requires_async=requires_async

releasenotes/notes/fix-openai-agent-snapshot-init-1ca26789564a53fe.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Prevent duplication of the last assistant message in the chat history when initializing from an `AgentSnapshot`.

test/components/agents/test_agent.py

@@ -141,7 +141,7 @@ def to_dict(self) -> dict[str, Any]:
         return {"type": "MockChatGeneratorWithoutRunAsync", "data": {}}
 
     @classmethod
-    def from_dict(cls, data: dict[str, Any]) -> "MockChatGeneratorWithoutRunAsync":
+    def from_dict(cls, data: dict[str, Any]) -> "MockChatGenerator":
         return cls()
 
     @component.output_types(replies=list[ChatMessage])