Visual Studio File Nesting for gRPC proto files

I have a load of .proto files that generate an associated .cs file, and i also have a partial .cs file, all of the same name:

1. message.proto
2. message.cs (autogenerated in the obj\debug directory)
3. mesasge.cs (in the same folder as the proto file)

I am trying to get them nesting with Visual Studio 2019, but unable. Pointers much appreciated as to what i am doing wrong.

{
  "help": "https://go.microsoft.com/fwlink/?linkid=866610",
  "root": true,

  "dependentFileProviders": {
    "add": {
      "addedExtension": {},
      "pathSegment": {
        "add": {
          ".*": [
            ".js",
            ".css",
            ".html",
            ".htm",
            ".less",
            ".scss",
            ".coffee",
            ".iced",
            ".config",
            ".cs",
            ".vb",
            ".json",
            ".proto"
          ]
        }
      },
      "extensionToExtension": {
        "add": {
          ".proto": [
            ".cs"
          ],
          ".js": [
            ".coffee",
            ".iced",
            ".ts",
            ".tsx",
            ".jsx"
          ],
          ".css": [
            ".less",
            ".scss",
            ".sass",
            ".styl"
          ],
          ".html": [
            ".md",
            ".mdown",
            ".markdown",
            ".mdwn"
          ],
          ".map": [
            ".js",
            ".css"
          ],
          ".svgz": [
            ".svg"
          ],
          ".designer.cs": [
            ".resx"
          ],
          ".cs.d.ts": [
            ".cs"
          ]
        }
      },
      "fileToFile": {
        "add": {
          ".bowerrc": [
            "bower.json"
          ],
          ".npmrc": [
            "package.json"
          ],
          "npm-shrinkwrap.json": [
            "package.json"
          ],
          "yarn.lock": [
            "package.json"
          ],
          ".yarnclean": [
            "package.json"
          ],
          ".yarnignore": [
            "package.json"
          ],
          ".yarn-integrity": [
            "package.json"
          ],
          ".yarnrc": [
            "package.json"
          ],
          "package-lock.json": [
            "package.json"
          ]
        }
      },
      "fileSuffixToExtension": {
        "add": {
          "-vsdoc.js": [
            ".js"
          ]
        }
      },
      "allExtensions": {
        "add": {
          ".*": [
            ".tt"
          ]
        }
      }
    }
  }
}