Type error when decoding `timestamp` in `ProjectFromId` transformation with `S.DateFromNumber`

export class Project extends S.Class<Project>("Project")({
  id: withDefaultId(ProjectId),
  code: S.String,
  subCode: S.optional(S.String),
  description: S.optional(S.String),
  requiresClient: S.Boolean.pipe(withDefault(() => false)),
  timestamp: S.DateFromNumber.pipe(withDefault(() => new Date()))
}) {}

//...

export const ProjectFromId = S.transformOrFail(ProjectId, Project, {
  strict: true,

  decode: (id, _, ast) =>
    E.gen(function*() {
      const projects = yield* ProvidedProjects
      const project = yield* projects.find(id)

      // this doesn't work
      // return project

      // but this does, which doesn't make sense - timestamp is `S.DateFromNumber`
      // so the _encoded_ timestamp is a number, the _decoded_ timestamp is a date
      // but it's only happy here if I coerce timestamp back to a number

      return {
        ...project,
        timestamp: project.timestamp instanceof Date ? project.timestamp.getTime() : project.timestamp
      }
    }).pipe(E.mapError((error) => new ParseResult.Type(ast, id, error.message))),

  encode: (p) => ParseResult.succeed(ProjectId.make(p.id))
})