message: throw on failed insert
diff: @@ -2278,6 +2278,14 @@ export class MergeTree {
  const splitNode = this.insertingWalk(this.root, insertPos, refSeq, clientId, seq,
  { leaf: onLeaf, candidateSegment: newSegment, continuePredicate: continueFrom });
  + if(newSegment.parent === undefined){
  + throw new Error(`MergeTree insert failed: ${JSON.stringify({
  + currentSeq: this.collabWindow.currentSeq,
  + minSeq: this.collabWindow.minSeq,
  + segSeq: newSegment.seq,
  + })}`);
  + }
  +
  this.updateRoot(splitNode);
  saveIfLocal(newSegment);
  