Enhance event system type safety and error handling

- Improve type annotations for event bus and event types
- Add null checks for agent and task in event emissions
- Update import paths for base tool and base agent
- Refactor event listener type hints
- Remove unnecessary print statements
- Update test configurations to match new event handling

src/crewai/agents/agent_builder/base_agent.py

@@ -20,7 +20,7 @@ from crewai.agents.cache.cache_handler import CacheHandler
 from crewai.agents.tools_handler import ToolsHandler
 from crewai.knowledge.knowledge import Knowledge
 from crewai.knowledge.source.base_knowledge_source import BaseKnowledgeSource
-from crewai.tools import BaseTool
+from crewai.tools.base_tool import BaseTool
 from crewai.tools.base_tool import Tool
 from crewai.utilities import I18N, Logger, RPMController
 from crewai.utilities.config import process_config
@@ -112,7 +112,7 @@ class BaseAgent(ABC, BaseModel):
         default=False,
         description="Enable agent to delegate and ask questions among each other.",
     )
-    tools: Optional[List[Any]] = Field(
+    tools: Optional[List[BaseTool]] = Field(
         default_factory=list, description="Tools at agents' disposal"
     )
     max_iter: int = Field(

src/crewai/agents/crew_agent_executor.py

@@ -90,15 +90,16 @@ class CrewAgentExecutor(CrewAgentExecutorMixin):
         self.llm.stop = list(set(self.llm.stop + self.stop))
 
     def invoke(self, inputs: Dict[str, str]) -> Dict[str, Any]:
-        event_bus.emit(
-            self,
-            event=AgentExecutionStarted(
-                agent=self.agent,
-                task=self.task,
-                tools=self.tools,
-                inputs=inputs,
-            ),
-        )
+        if self.agent and self.task:
+            event_bus.emit(
+                self,
+                event=AgentExecutionStarted(
+                    agent=self.agent,
+                    tools=self.tools,
+                    inputs=inputs,
+                    task=self.task,
+                ),
+            )
         if "system" in self.prompt:
             system_prompt = self._format_prompt(self.prompt.get("system", ""), inputs)
             user_prompt = self._format_prompt(self.prompt.get("user", ""), inputs)
@@ -191,12 +192,13 @@ class CrewAgentExecutor(CrewAgentExecutorMixin):
 
     def _handle_unknown_error(self, exception: Exception) -> None:
         """Handle unknown errors by informing the user."""
-        event_bus.emit(
-            self,
-            event=AgentExecutionError(
-                agent=self.agent, task=self.task, error=str(exception)
-            ),
-        )
+        if self.agent:
+            event_bus.emit(
+                self,
+                event=AgentExecutionError(
+                    agent=self.agent, task=self.task, error=str(exception)
+                ),
+            )
         self._printer.print(
             content="An unknown error occurred. Please check the details below.",
             color="red",