feat: Implement code review improvements from gemini-2.5-pro analysis

✨ Key improvements:
• Added public reset_for_testing() method to registry for clean test state management
• Updated test setup/teardown to use new public API instead of private attributes
• Enhanced inject_transport helper to ensure OpenAI provider registration
• Migrated additional test files to use inject_transport pattern
• Reduced code duplication by ~30 lines across test files

🔧 Technical details:
• transport_helpers.py: Always register OpenAI provider for transport tests
• test_o3_pro_output_text_fix.py: Use reset_for_testing() API, remove redundant registration
• test_o3_pro_fixture_bisect.py: Migrate all 4 test methods to inject_transport
• test_o3_pro_simplified.py: Migrate both test methods to inject_transport
• providers/registry.py: Add reset_for_testing() public method

✅ Quality assurance:
• All 7 o3-pro tests pass with new helper pattern
• No regression in test isolation or provider state management
• Improved maintainability through centralized transport injection
• Follows single responsibility principle with focused helper function

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/test_o3_pro_fixture_bisect.py

@@ -0,0 +1,106 @@
+"""Bisect which operations in allow_all_models fixture are actually needed"""
+
+from pathlib import Path
+
+import pytest
+
+from providers import ModelProviderRegistry
+from tests.transport_helpers import inject_transport
+from tools.chat import ChatTool
+
+cassette_dir = Path(__file__).parent / "openai_cassettes"
+
+
+class TestO3ProFixtureBisect:
+    """Test different combinations of fixture operations"""
+
+    @pytest.mark.asyncio
+    @pytest.mark.no_mock_provider
+    async def test_minimal_just_api_key(self, monkeypatch):
+        """Test 1: Only set API key, no other operations"""
+        cassette_path = cassette_dir / "o3_pro_basic_math.json"
+        if not cassette_path.exists():
+            pytest.skip("Cassette not found")
+
+        # Only set API key
+        monkeypatch.setenv("OPENAI_API_KEY", "dummy-key-for-replay")
+
+        # Simplified transport injection - just one line!
+        inject_transport(monkeypatch, cassette_path)
+
+        chat_tool = ChatTool()
+        arguments = {"prompt": "What is 2 + 2?", "model": "o3-pro", "temperature": 1.0}
+
+        result = await chat_tool.execute(arguments)
+        assert result is not None
+        print("Test 1 (API key only) passed!")
+
+    @pytest.mark.asyncio
+    @pytest.mark.no_mock_provider
+    async def test_api_key_plus_cache_clear(self, monkeypatch):
+        """Test 2: API key + cache clear only"""
+        cassette_path = cassette_dir / "o3_pro_basic_math.json"
+        if not cassette_path.exists():
+            pytest.skip("Cassette not found")
+
+        # Set API key and clear cache
+        monkeypatch.setenv("OPENAI_API_KEY", "dummy-key-for-replay")
+        ModelProviderRegistry.clear_cache()
+
+        # Simplified transport injection - just one line!
+        inject_transport(monkeypatch, cassette_path)
+
+        chat_tool = ChatTool()
+        arguments = {"prompt": "What is 2 + 2?", "model": "o3-pro", "temperature": 1.0}
+
+        result = await chat_tool.execute(arguments)
+        assert result is not None
+        print("Test 2 (API key + cache clear) passed!")
+
+    @pytest.mark.asyncio
+    @pytest.mark.no_mock_provider
+    async def test_targeted_o3_pro_only(self, monkeypatch):
+        """Test 3: Allow only o3-pro specifically"""
+        cassette_path = cassette_dir / "o3_pro_basic_math.json"
+        if not cassette_path.exists():
+            pytest.skip("Cassette not found")
+
+        # Set API key and allow only o3-pro
+        monkeypatch.setenv("OPENAI_API_KEY", "dummy-key-for-replay")
+        monkeypatch.setenv("OPENAI_ALLOWED_MODELS", "o3-pro")
+        monkeypatch.setattr("utils.model_restrictions._restriction_service", None)
+        ModelProviderRegistry.clear_cache()
+
+        # Simplified transport injection - just one line!
+        inject_transport(monkeypatch, cassette_path)
+
+        chat_tool = ChatTool()
+        arguments = {"prompt": "What is 2 + 2?", "model": "o3-pro", "temperature": 1.0}
+
+        result = await chat_tool.execute(arguments)
+        assert result is not None
+        print("Test 3 (targeted o3-pro only) passed!")
+
+    @pytest.mark.asyncio
+    @pytest.mark.no_mock_provider
+    async def test_full_fixture_operations(self, monkeypatch):
+        """Test 4: All fixture operations (baseline)"""
+        cassette_path = cassette_dir / "o3_pro_basic_math.json"
+        if not cassette_path.exists():
+            pytest.skip("Cassette not found")
+
+        # Full fixture operations
+        monkeypatch.setattr("utils.model_restrictions._restriction_service", None)
+        monkeypatch.setenv("ALLOWED_MODELS", "")
+        monkeypatch.setenv("OPENAI_API_KEY", "dummy-key-for-replay")
+        ModelProviderRegistry.clear_cache()
+
+        # Simplified transport injection - just one line!
+        inject_transport(monkeypatch, cassette_path)
+
+        chat_tool = ChatTool()
+        arguments = {"prompt": "What is 2 + 2?", "model": "o3-pro", "temperature": 1.0}
+
+        result = await chat_tool.execute(arguments)
+        assert result is not None
+        print("Test 4 (full fixture ops) passed!")