feat(mcp): implement Gemini dual-transport validation

Add comprehensive validation for Gemini's dual-transport capability supporting
both SSE (with 'url' field) and HTTP (with 'httpUrl' field) transports.

Key changes:
- Override parent transport validator in MCPServerConfigGemini
- Validate mutual exclusion of 'url' and 'httpUrl' fields
- Support type inference from transport fields
- Add 3 comprehensive validation tests

Gemini now supports:
- stdio transport with 'command' field
- sse transport with 'url' field
- http transport with 'httpUrl' field

Fixes: Issue 3 - Gemini dual-transport validation

Author: LittleCoinCoin

hatch/mcp_host_config/models.py

@@ -360,7 +360,14 @@ class MCPServerConfigBase(BaseModel):
 
     @model_validator(mode='after')
     def validate_transport(self) -> 'MCPServerConfigBase':
-        """Validate transport configuration using type field."""
+        """Validate transport configuration using type field.
+
+        Note: Gemini subclass overrides this with dual-transport support.
+        """
+        # Skip validation for Gemini which has its own dual-transport validator
+        if self.__class__.__name__ == 'MCPServerConfigGemini':
+            return self
+
         # Check mutual exclusion - command and url cannot both be set
         if self.command is not None and self.url is not None:
             raise ValueError(
@@ -413,6 +420,45 @@ class MCPServerConfigGemini(MCPServerConfigBase):
     oauth_audiences: Optional[List[str]] = Field(None, description="OAuth audiences")
     authProviderType: Optional[str] = Field(None, description="Authentication provider type")
 
+    @model_validator(mode='after')
+    def validate_gemini_dual_transport(self):
+        """Override transport validation to support Gemini's dual-transport capability.
+
+        Gemini supports both:
+        - SSE transport with 'url' field
+        - HTTP transport with 'httpUrl' field
+
+        Validates that:
+        1. Either url or httpUrl is provided (not both)
+        2. Type field matches the transport being used
+        """
+        # Check if both url and httpUrl are provided
+        if self.url is not None and self.httpUrl is not None:
+            raise ValueError("Cannot specify both 'url' and 'httpUrl' - choose one transport")
+
+        # Validate based on type
+        if self.type == "stdio":
+            if not self.command:
+                raise ValueError("'command' is required for stdio transport")
+        elif self.type == "sse":
+            if not self.url:
+                raise ValueError("'url' is required for sse transport")
+        elif self.type == "http":
+            if not self.httpUrl:
+                raise ValueError("'httpUrl' is required for http transport")
+        elif self.type is None:
+            # Infer type from fields if not specified
+            if self.command:
+                self.type = "stdio"
+            elif self.url:
+                self.type = "sse"  # default to sse for url
+            elif self.httpUrl:
+                self.type = "http"  # http for httpUrl
+            else:
+                raise ValueError("Either 'command', 'url', or 'httpUrl' must be provided")
+
+        return self
+
     @classmethod
     def from_omni(cls, omni: 'MCPServerConfigOmni') -> 'MCPServerConfigGemini':
         """Convert Omni model to Gemini-specific model using Pydantic APIs."""

tests/test_mcp_cli_partial_updates.py

@@ -626,9 +626,9 @@ def test_partial_update_end_to_end_switch_type(self):
                 with patch('hatch.cli_hatch.generate_conversion_report') as mock_report:
                     mock_report.return_value = MagicMock()
 
-                    # Execute: Switch to URL-based
+                    # Execute: Switch to URL-based (use gemini which supports URL)
                     result = handle_mcp_configure(
-                        host="claude-desktop",
+                        host="gemini",
                         server_name="test-server",
                         command=None,
                         args=None,

tests/test_mcp_pydantic_architecture_v4.py

@@ -556,6 +556,48 @@ def test_claude_from_omni_with_universal_fields(self):
         self.assertEqual(claude.env["API_KEY"], "test")
 
 
+class TestGeminiDualTransport(unittest.TestCase):
+    """Test suite for Gemini dual-transport validation (Issue 3)."""
+
+    @regression_test
+    def test_gemini_sse_transport_with_url(self):
+        """Test Gemini SSE transport uses url field."""
+        config = MCPServerConfigGemini(
+            name="gemini-server",
+            type="sse",
+            url="https://api.example.com/mcp"
+        )
+
+        self.assertEqual(config.type, "sse")
+        self.assertEqual(config.url, "https://api.example.com/mcp")
+        self.assertIsNone(config.httpUrl)
+
+    @regression_test
+    def test_gemini_http_transport_with_httpUrl(self):
+        """Test Gemini HTTP transport uses httpUrl field."""
+        config = MCPServerConfigGemini(
+            name="gemini-server",
+            type="http",
+            httpUrl="https://api.example.com/mcp"
+        )
+
+        self.assertEqual(config.type, "http")
+        self.assertEqual(config.httpUrl, "https://api.example.com/mcp")
+        self.assertIsNone(config.url)
+
+    @regression_test
+    def test_gemini_mutual_exclusion_url_and_httpUrl(self):
+        """Test Gemini rejects both url and httpUrl simultaneously."""
+        with self.assertRaises(ValidationError) as context:
+            MCPServerConfigGemini(
+                name="gemini-server",
+                url="https://api.example.com/sse",
+                httpUrl="https://api.example.com/http"
+            )
+
+        self.assertIn("Cannot specify both 'url' and 'httpUrl'", str(context.exception))
+
+
 if __name__ == '__main__':
     unittest.main()