refactor: clean up agent architecture and coordination loop

Squash merged refactoring of agent architecture.

tests/test_best_practices.py

@@ -94,7 +94,8 @@ def test_run_verification_failure(tmp_path: Path) -> None:
 
 
 @patch("core.dispatcher.CodingAgent")
-async def test_dispatch_planning_and_coding_phases(mock_agent_class: MagicMock) -> None:
+@patch("core.dispatcher.PlanningAgent")
+async def test_dispatch_planning_and_coding_phases(mock_planning_class: MagicMock, mock_coding_class: MagicMock) -> None:
     mock_client: MagicMock = MagicMock(spec=GiteaClient)
     mock_tools: MagicMock = MagicMock(spec=GiteaTools)
 
@@ -117,14 +118,14 @@ async def test_dispatch_planning_and_coding_phases(mock_agent_class: MagicMock)
     mock_client.get_pull_request_files.return_value = []
     mock_client.get_pr_reviews.return_value = []
 
-    # Mock CodingAgent instances
+    # Mock agent instances
     mock_planning_agent = MagicMock()
     mock_planning_agent.run_with_tools = AsyncMock(return_value="Plan: Modify file A")
+    mock_planning_class.return_value = mock_planning_agent
 
     mock_coding_agent = MagicMock()
     mock_coding_agent.run_with_tools = AsyncMock(return_value="PR #1 Created")
-
-    mock_agent_class.side_effect = [mock_planning_agent, mock_coding_agent]
+    mock_coding_class.return_value = mock_coding_agent
 
     dispatcher = AgentDispatcher(client=mock_client, tools=mock_tools)