refactor: Simplify o3-pro test by removing fixture and monkey patching boilerplate

- Remove over-engineered allow_all_models fixture (6 operations → 1 line API key setting)
- Replace 10 lines of monkey patching boilerplate with 1-line inject_transport helper
- Remove cargo-cult error handling that allowed test to pass with API failures
- Create reusable transport_helpers.py for HTTP transport injection patterns
- Fix provider registration state pollution between batch test runs
- Test now works reliably in both individual and batch execution modes

The test is significantly cleaner and addresses root cause (provider registration timing)
rather than symptoms (cache clearing).

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

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

tests/transport_helpers.py

@@ -0,0 +1,47 @@
+"""Helper functions for HTTP transport injection in tests."""
+
+from tests.http_transport_recorder import TransportFactory
+
+
+def inject_transport(monkeypatch, cassette_path: str):
+    """Inject HTTP transport into OpenAICompatibleProvider for testing.
+
+    This helper simplifies the monkey patching pattern used across tests
+    to inject custom HTTP transports for recording/replaying API calls.
+    
+    Also ensures OpenAI provider is properly registered for tests that need it.
+
+    Args:
+        monkeypatch: pytest monkeypatch fixture
+        cassette_path: Path to cassette file for recording/replay
+
+    Returns:
+        The created transport instance
+
+    Example:
+        transport = inject_transport(monkeypatch, "path/to/cassette.json")
+    """
+    # Ensure OpenAI provider is registered if API key is available
+    import os
+    if os.getenv("OPENAI_API_KEY"):
+        from providers.registry import ModelProviderRegistry
+        from providers.base import ProviderType
+        from providers.openai_provider import OpenAIModelProvider
+        ModelProviderRegistry.register_provider(ProviderType.OPENAI, OpenAIModelProvider)
+    
+    # Create transport
+    transport = TransportFactory.create_transport(str(cassette_path))
+
+    # Inject transport using the established pattern
+    from providers.openai_compatible import OpenAICompatibleProvider
+
+    original_client_property = OpenAICompatibleProvider.client
+
+    def patched_client_getter(self):
+        if self._client is None:
+            self._test_transport = transport
+        return original_client_property.fget(self)
+
+    monkeypatch.setattr(OpenAICompatibleProvider, "client", property(patched_client_getter))
+
+    return transport