Crash if duplicate model names (across files) used in allOf

[mikeharder]

A TSP conversion PR resulted in this error:

"details":"incompatible properties : tags

definitions/ContainerGroup/properties/tags
 at file:///home/runner/work/azure-rest-api-specs/azure-rest-api-specs/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/ContainerInstance/stable/2025-09-01/containerInstance.json#L2245:8

definitions/Resource/properties/tags
  at file:///home/runner/work/azure-rest-api-specs/azure-rest-api-specs/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/ContainerInstance/stable/2025-09-01/containerInstance.json#L4642:8"

• https://github.com/Azure/azure-rest-api-specs/actions/runs/23628050434
• Migrate Containerinstance to TypeSpec azure-rest-api-specs#41602

Root cause, oad cannot handle two definitions in different files with the same name, if one definition is used in an allOf:

duplicate-names.json

{
  "swagger": "2.0",
  "info": {
    "title": "duplicate-names",
    "version": "1.0"
  },
  "paths": {},
  "definitions": {
    "Bar": {
      "type": "object",
      "properties": {
        "p1": {
          "type": "string"
        }
      },
      "allOf": [
        {
          "$ref": "./common-types.json#/definitions/Foo"
        }
      ]
    },
    "Foo": {
      "type": "object",
      "properties": {
        "p1": {
          "type": "object"
        }
      }
    }
  }
}

common-types.json

{
  "swagger": "2.0",
  "info": {
    "title": "common-types",
    "version": "1.0"
  },
  "paths": {},
  "definitions": {
    "Foo": {
      "type": "object",
      "properties": {
        "p1": {
          "type": "string"
        }
      }
    }
  }
}

test result

    incompatible properties : p1
      definitions/Bar/properties/p1
        at file:///home/mharder/openapi-diff-mh/incompat-prop/src/test/specs/incompatible-properties/duplicate-names.json#L12:8
      definitions/Foo/properties/p1
        at file:///home/mharder/openapi-diff-mh/incompat-prop/src/test/specs/incompatible-properties/duplicate-names.json#L25:8

• Test case: Allow allOf properties that are structurally equal #481

Reason, it assumes model names are unique across all files:

openapi-diff/src/lib/util/resolveSwagger.ts

Lines 346 to 352 in bb4653d

	private getModelName(ref: string) {
	const parts = ref.split("/")
	if (parts.length === 3 && parts[1] === "definitions") {
	return parts[2]
	}
	return undefined
	}

Related: #347