fix: manager delegation bug in hierarchical mode (Issue #1823)

- Fix manager agent delegation tool generation in hierarchical mode
- Add comprehensive test suite for delegation scenarios
- Ensure manager can delegate to all agents regardless of task assignment

Co-Authored-By: Joe Moura <joao@crewai.com>

tests/test_hierarchical_delegation.py

@@ -0,0 +1,126 @@
+import pytest
+from unittest.mock import MagicMock, patch
+from crewai.agent import Agent
+from crewai.crew import Crew
+from crewai.task import Task
+from crewai.process import Process
+from crewai.tools.agent_tools.agent_tools import AgentTools
+
+def test_manager_delegation_with_task_agent():
+    """Test that manager can delegate to all agents even when task.agent is specified."""
+    # Create mock LLM
+    mock_llm = MagicMock()
+    
+    # Create agents
+    manager = Agent(
+        role="Manager",
+        goal="Manage the team",
+        backstory="I am the manager",
+        allow_delegation=True,
+        llm=mock_llm,
+    )
+    
+    agent1 = Agent(
+        role="Agent1",
+        goal="Do task 1",
+        backstory="I am agent 1",
+        llm=mock_llm,
+    )
+    
+    agent2 = Agent(
+        role="Agent2",
+        goal="Do task 2",
+        backstory="I am agent 2",
+        llm=mock_llm,
+    )
+    
+    # Create task with specific agent
+    task = Task(
+        description="Test task",
+        expected_output="Test output",  # Required field
+        agent=agent1
+    )
+    
+    # Create crew in hierarchical mode
+    crew = Crew(
+        agents=[agent1, agent2],
+        tasks=[task],
+        manager_agent=manager,
+        process=Process.hierarchical,
+    )
+    
+    # Get tools that would be available to the manager
+    tools = crew._update_manager_tools(task, [])
+    
+    # Extract delegation tool
+    from crewai.tools.agent_tools.delegate_work_tool import DelegateWorkTool
+    delegation_tools = [t for t in tools if isinstance(t, DelegateWorkTool)]
+    assert len(delegation_tools) > 0, "No delegation tools found"
+    
+    # Verify all agents are available for delegation
+    delegation_tool = delegation_tools[0]
+    available_agents = delegation_tool.agents
+    
+    # Manager should see both agents as delegation targets
+    assert len(available_agents) == 2, "Manager should see all agents"
+    assert agent1 in available_agents, "Agent1 should be available for delegation"
+    assert agent2 in available_agents, "Agent2 should be available for delegation"
+
+def test_manager_delegation_without_task_agent():
+    """Test that manager can delegate to all agents when no task.agent is specified."""
+    # Create mock LLM
+    mock_llm = MagicMock()
+    
+    # Create agents
+    manager = Agent(
+        role="Manager",
+        goal="Manage the team",
+        backstory="I am the manager",
+        allow_delegation=True,
+        llm=mock_llm,
+    )
+    
+    agent1 = Agent(
+        role="Agent1",
+        goal="Do task 1",
+        backstory="I am agent 1",
+        llm=mock_llm,
+    )
+    
+    agent2 = Agent(
+        role="Agent2",
+        goal="Do task 2",
+        backstory="I am agent 2",
+        llm=mock_llm,
+    )
+    
+    # Create task without specific agent
+    task = Task(
+        description="Test task",
+        expected_output="Test output"  # Required field
+    )
+    
+    # Create crew in hierarchical mode
+    crew = Crew(
+        agents=[agent1, agent2],
+        tasks=[task],
+        manager_agent=manager,
+        process=Process.hierarchical,
+    )
+    
+    # Get tools that would be available to the manager
+    tools = crew._update_manager_tools(task, [])
+    
+    # Extract delegation tool
+    from crewai.tools.agent_tools.delegate_work_tool import DelegateWorkTool
+    delegation_tools = [t for t in tools if isinstance(t, DelegateWorkTool)]
+    assert len(delegation_tools) > 0, "No delegation tools found"
+    
+    # Verify all agents are available for delegation
+    delegation_tool = delegation_tools[0]
+    available_agents = delegation_tool.agents
+    
+    # Manager should see both agents as delegation targets
+    assert len(available_agents) == 2, "Manager should see all agents"
+    assert agent1 in available_agents, "Agent1 should be available for delegation"
+    assert agent2 in available_agents, "Agent2 should be available for delegation"