fix: Add mdstream mock to resolve WholeFileCoder test failure

tests/basic/test_reasoning.py

@@ -121,6 +121,9 @@ class TestReasoning(unittest.TestCase):
 
         # Mock the model's send_completion to return the hash and completion
         with patch.object(model, "send_completion", return_value=(mock_hash, chunks)):
+            # Set mdstream directly on the coder object
+            coder.mdstream = mock_mdstream
+            
             # Call send with a simple message
             messages = [{"role": "user", "content": "test prompt"}]
             list(coder.send(messages))