Children are listed in subtree order (escaped segment + separator) so the skip-scan stays O(children) even when sibling keys extend each other with characters below the separator. Model-based property test vs a reference Map. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017Qxbkp4tA7G5SCWjzWuxmE