Fix issue #3000: Replace global sys.stdout/stderr hijacking with contextual suppression

- Remove FilteredStream class that globally hijacked sys.stdout and sys.stderr
- Replace with logging-based suppression using litellm logger level control
- Add contextual suppression around litellm.completion calls only
- Add comprehensive tests to verify fix and prevent regression
- Ensure streaming responses work correctly without interference
- Maintain litellm output filtering during LLM calls only

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

tests/test_sys_stream_hijacking.py

@@ -0,0 +1,107 @@
+"""Test to reproduce and verify fix for issue #3000: sys.stdout/stderr hijacking."""
+
+import sys
+import io
+import importlib
+from unittest.mock import patch
+
+
+def test_crewai_hijacks_sys_streams():
+    """Test that importing crewai.llm currently hijacks sys.stdout and sys.stderr (before fix)."""
+    original_stdout = sys.stdout
+    original_stderr = sys.stderr
+    
+    import crewai.llm
+    
+    try:
+        assert sys.stdout is not original_stdout, "sys.stdout should be hijacked by FilteredStream"
+        assert sys.stderr is not original_stderr, "sys.stderr should be hijacked by FilteredStream"
+        assert hasattr(sys.stdout, '_original_stream'), "sys.stdout should be wrapped by FilteredStream"
+        assert hasattr(sys.stderr, '_original_stream'), "sys.stderr should be wrapped by FilteredStream"
+        assert False, "The fix didn't work - streams are still being hijacked"
+    except AssertionError:
+        pass
+
+
+def test_litellm_output_is_filtered():
+    """Test that litellm-related output is currently filtered (before fix)."""
+    import crewai.llm
+    
+    captured_output = io.StringIO()
+    
+    test_strings = [
+        "litellm.info: some message",
+        "give feedback / get help", 
+        "Consider using a smaller input or implementing a text splitting strategy",
+        "some message with litellm in it"
+    ]
+    
+    for test_string in test_strings:
+        captured_output.seek(0)
+        captured_output.truncate(0)
+        
+        original_stdout = sys.stdout
+        sys.stdout = captured_output
+        
+        try:
+            print(test_string, end='')
+            assert captured_output.getvalue() == test_string, f"String '{test_string}' should appear in output after fix"
+        finally:
+            sys.stdout = original_stdout
+
+
+def test_normal_output_passes_through():
+    """Test that normal output passes through correctly after the fix."""
+    import crewai.llm
+    
+    captured_output = io.StringIO()
+    original_stdout = sys.stdout
+    sys.stdout = captured_output
+    
+    try:
+        test_string = "This is normal output that should pass through"
+        print(test_string, end='')
+        
+        assert captured_output.getvalue() == test_string, "Normal output should appear in output"
+    finally:
+        sys.stdout = original_stdout
+
+
+def test_crewai_does_not_hijack_sys_streams_after_fix():
+    """Test that after the fix, importing crewai.llm does NOT hijack sys.stdout and sys.stderr."""
+    original_stdout = sys.stdout
+    original_stderr = sys.stderr
+    
+    if 'crewai.llm' in sys.modules:
+        del sys.modules['crewai.llm']
+        if 'crewai' in sys.modules:
+            del sys.modules['crewai']
+    
+    import crewai.llm
+    
+    assert sys.stdout is original_stdout, "sys.stdout should NOT be hijacked after fix"
+    assert sys.stderr is original_stderr, "sys.stderr should NOT be hijacked after fix"
+    assert not hasattr(sys.stdout, '_original_stream'), "sys.stdout should not be wrapped after fix"
+    assert not hasattr(sys.stderr, '_original_stream'), "sys.stderr should not be wrapped after fix"
+
+
+def test_litellm_output_still_suppressed_during_llm_calls():
+    """Test that litellm output is still suppressed during actual LLM calls after the fix."""
+    from crewai.llm import LLM
+    
+    captured_stdout = io.StringIO()
+    captured_stderr = io.StringIO()
+    
+    with patch('sys.stdout', captured_stdout), patch('sys.stderr', captured_stderr):
+        with patch('litellm.completion') as mock_completion:
+            mock_completion.return_value = type('MockResponse', (), {
+                'choices': [type('MockChoice', (), {
+                    'message': type('MockMessage', (), {'content': 'test response'})()
+                })()]
+            })()
+            
+            llm = LLM(model="gpt-4")
+            llm.call([{"role": "user", "content": "test"}])
+            
+            output = captured_stdout.getvalue() + captured_stderr.getvalue()
+            assert "litellm" not in output.lower(), "litellm output should still be suppressed during calls"