Add comprehensive OpenAPI 3.0 vs 3.1 compatibility tests

Adds test coverage for specific differences between OpenAPI 3.0 and 3.1 that can cause validation issues, including the scenario reported in GitHub issue #1021.

Test coverage includes:
- OpenAPI 3.0 boolean exclusiveMaximum format vs 3.1 numeric format
- OpenAPI 3.0 nullable vs 3.1 type array format
- Complex schemas with $defs and multiple exclusive constraints
- Edge cases with both exclusiveMaximum and exclusiveMinimum

These tests serve as regression prevention and document expected behavior for both OpenAPI versions.

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

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

tests/server/openapi/test_openapi_compatibility.py

@@ -369,3 +369,312 @@ class TestOpenAPI31Compatibility:
             assert result.data["id"] == "o3"
             assert result.data["customer"] == "Charlie"
             assert result.data["items"] == ["item4", "item5"]
+
+
+class TestOpenAPIVersionDifferences:
+    """Test specific differences between OpenAPI 3.0 and 3.1 that can cause compatibility issues."""
+
+    def test_openapi_30_exclusive_maximum_boolean_format(self):
+        """Test OpenAPI 3.0 format with boolean exclusiveMaximum (reproduces GitHub issue #1021)."""
+        spec_with_exclusive_max = {
+            "openapi": "3.0.0",
+            "info": {"title": "Loan API", "version": "1.0.0"},
+            "paths": {
+                "/loans": {
+                    "post": {
+                        "operationId": "createLoan",
+                        "summary": "Create a loan",
+                        "requestBody": {
+                            "required": True,
+                            "content": {
+                                "application/json": {
+                                    "schema": {
+                                        "$ref": "#/components/schemas/LoanDetails"
+                                    }
+                                }
+                            },
+                        },
+                        "responses": {"201": {"description": "Loan created"}},
+                    }
+                }
+            },
+            "components": {
+                "schemas": {
+                    "LoanDetails": {
+                        "type": "object",
+                        "properties": {
+                            "amount": {"type": "number", "minimum": 0},
+                            "interest_rate": {
+                                "type": "number",
+                                "minimum": 0,
+                                "maximum": 100,
+                                "exclusiveMaximum": True,  # OpenAPI 3.0 boolean format
+                            },
+                        },
+                        "required": ["amount", "interest_rate"],
+                    }
+                }
+            },
+        }
+
+        # This should not raise a ValidationError
+        from fastmcp.utilities.openapi import parse_openapi_to_http_routes
+
+        routes = parse_openapi_to_http_routes(spec_with_exclusive_max)
+        assert len(routes) == 1
+        assert routes[0].operation_id == "createLoan"
+
+    def test_openapi_31_exclusive_maximum_numeric_format(self):
+        """Test OpenAPI 3.1 format with numeric exclusiveMaximum."""
+        spec_with_exclusive_max = {
+            "openapi": "3.1.0",
+            "info": {"title": "Loan API", "version": "1.0.0"},
+            "paths": {
+                "/loans": {
+                    "post": {
+                        "operationId": "createLoan",
+                        "summary": "Create a loan",
+                        "requestBody": {
+                            "required": True,
+                            "content": {
+                                "application/json": {
+                                    "schema": {
+                                        "$ref": "#/components/schemas/LoanDetails"
+                                    }
+                                }
+                            },
+                        },
+                        "responses": {"201": {"description": "Loan created"}},
+                    }
+                }
+            },
+            "components": {
+                "schemas": {
+                    "LoanDetails": {
+                        "type": "object",
+                        "properties": {
+                            "amount": {"type": "number", "minimum": 0},
+                            "interest_rate": {
+                                "type": "number",
+                                "minimum": 0,
+                                "exclusiveMaximum": 100,  # OpenAPI 3.1 numeric format
+                            },
+                        },
+                        "required": ["amount", "interest_rate"],
+                    }
+                }
+            },
+        }
+
+        # This should not raise a ValidationError
+        from fastmcp.utilities.openapi import parse_openapi_to_http_routes
+
+        routes = parse_openapi_to_http_routes(spec_with_exclusive_max)
+        assert len(routes) == 1
+        assert routes[0].operation_id == "createLoan"
+
+    def test_openapi_30_nullable_format(self):
+        """Test OpenAPI 3.0 nullable format."""
+        spec_with_nullable = {
+            "openapi": "3.0.0",
+            "info": {"title": "User API", "version": "1.0.0"},
+            "paths": {
+                "/users": {
+                    "post": {
+                        "operationId": "createUser",
+                        "summary": "Create a user",
+                        "requestBody": {
+                            "required": True,
+                            "content": {
+                                "application/json": {
+                                    "schema": {
+                                        "type": "object",
+                                        "properties": {
+                                            "name": {"type": "string"},
+                                            "email": {
+                                                "type": "string",
+                                                "nullable": True,  # OpenAPI 3.0 nullable format
+                                            },
+                                        },
+                                        "required": ["name"],
+                                    }
+                                }
+                            },
+                        },
+                        "responses": {"201": {"description": "User created"}},
+                    }
+                }
+            },
+        }
+
+        # This should not raise a ValidationError
+        from fastmcp.utilities.openapi import parse_openapi_to_http_routes
+
+        routes = parse_openapi_to_http_routes(spec_with_nullable)
+        assert len(routes) == 1
+        assert routes[0].operation_id == "createUser"
+
+    def test_openapi_31_type_array_format(self):
+        """Test OpenAPI 3.1 type array format for nullable values."""
+        spec_with_type_array = {
+            "openapi": "3.1.0",
+            "info": {"title": "User API", "version": "1.0.0"},
+            "paths": {
+                "/users": {
+                    "post": {
+                        "operationId": "createUser",
+                        "summary": "Create a user",
+                        "requestBody": {
+                            "required": True,
+                            "content": {
+                                "application/json": {
+                                    "schema": {
+                                        "type": "object",
+                                        "properties": {
+                                            "name": {"type": "string"},
+                                            "email": {
+                                                "type": [
+                                                    "string",
+                                                    "null",
+                                                ],  # OpenAPI 3.1 type array format
+                                            },
+                                        },
+                                        "required": ["name"],
+                                    }
+                                }
+                            },
+                        },
+                        "responses": {"201": {"description": "User created"}},
+                    }
+                }
+            },
+        }
+
+        # This should not raise a ValidationError
+        from fastmcp.utilities.openapi import parse_openapi_to_http_routes
+
+        routes = parse_openapi_to_http_routes(spec_with_type_array)
+        assert len(routes) == 1
+        assert routes[0].operation_id == "createUser"
+
+    def test_openapi_30_with_defs_and_exclusive_maximum(self):
+        """Test OpenAPI 3.0 with $defs and exclusiveMaximum (complex case from GitHub issue #1021)."""
+        spec_with_defs = {
+            "openapi": "3.0.0",
+            "info": {"title": "Complex Loan API", "version": "1.0.0"},
+            "paths": {
+                "/loans": {
+                    "post": {
+                        "operationId": "createComplexLoan",
+                        "summary": "Create a complex loan",
+                        "requestBody": {
+                            "required": True,
+                            "content": {
+                                "application/json": {
+                                    "schema": {
+                                        "type": "object",
+                                        "properties": {
+                                            "loanDetails": {
+                                                "$ref": "#/components/schemas/LoanDetails"
+                                            }
+                                        },
+                                        "required": ["loanDetails"],
+                                        "$defs": {
+                                            "LoanDetails": {
+                                                "type": "object",
+                                                "properties": {
+                                                    "interest_rate": {
+                                                        "type": "number",
+                                                        "minimum": 0,
+                                                        "maximum": 100,
+                                                        "exclusiveMaximum": True,  # This should trigger the issue
+                                                    },
+                                                },
+                                                "required": ["interest_rate"],
+                                            }
+                                        },
+                                    }
+                                }
+                            },
+                        },
+                        "responses": {"201": {"description": "Complex loan created"}},
+                    }
+                }
+            },
+            "components": {
+                "schemas": {
+                    "LoanDetails": {
+                        "type": "object",
+                        "properties": {
+                            "interest_rate": {
+                                "type": "number",
+                                "minimum": 0,
+                                "maximum": 100,
+                                "exclusiveMaximum": True,
+                            },
+                        },
+                        "required": ["interest_rate"],
+                    }
+                }
+            },
+        }
+
+        # This should reproduce the validation error from GitHub issue #1021
+        from fastmcp.utilities.openapi import parse_openapi_to_http_routes
+
+        try:
+            routes = parse_openapi_to_http_routes(spec_with_defs)
+            assert len(routes) == 1
+            assert routes[0].operation_id == "createComplexLoan"
+        except ValueError as e:
+            # If this fails, it's reproducing the issue
+            pytest.fail(f"OpenAPI 3.0 validation failed: {e}")
+
+    def test_openapi_30_edge_case_with_multiple_exclusive_constraints(self):
+        """Test edge case with multiple exclusive constraints that might trigger validation issues."""
+        spec_edge_case = {
+            "openapi": "3.0.0",
+            "info": {"title": "Edge Case API", "version": "1.0.0"},
+            "paths": {
+                "/validate": {
+                    "post": {
+                        "operationId": "validateData",
+                        "summary": "Validate data with edge case constraints",
+                        "requestBody": {
+                            "required": True,
+                            "content": {
+                                "application/json": {
+                                    "schema": {
+                                        "type": "object",
+                                        "properties": {
+                                            "percentage": {
+                                                "type": "number",
+                                                "minimum": 0,
+                                                "maximum": 100,
+                                                "exclusiveMaximum": True,
+                                                "exclusiveMinimum": True,  # Both exclusive constraints
+                                            },
+                                            "rating": {
+                                                "type": "integer",
+                                                "minimum": 1,
+                                                "maximum": 10,
+                                                "exclusiveMaximum": True,
+                                            },
+                                        },
+                                        "required": ["percentage", "rating"],
+                                    }
+                                }
+                            },
+                        },
+                        "responses": {"200": {"description": "Data validated"}},
+                    }
+                }
+            },
+        }
+
+        # This might trigger validation issues with multiple exclusive constraints
+        from fastmcp.utilities.openapi import parse_openapi_to_http_routes
+
+        routes = parse_openapi_to_http_routes(spec_edge_case)
+        assert len(routes) == 1
+        assert routes[0].operation_id == "validateData"