See discussion at https://chromium-review.googlesource.com/c/chromium/src/+/740973/7/docs/security/mojo.md#174:

"""Even better would be to enforce (1) with the type system, by creating a `Basename` type (distinct from `mojo.common.mojom.FilePath`) whose constructor(s), serializer(s), and deserializer(s) enforced the security property."""