message: don't allow range ops where start === end
diff: @@ -494,7 +494,7 @@ export class Client {
  // validate end if not insert, or insert has end
  //
  if (op.type !== ops.MergeTreeDeltaType.INSERT || end !== undefined) {
  - if (end === undefined || end < start) {
  + if (end === undefined || end <= start) {
  invalidPositions.push("end");
  }
  }
  