Pure ordering math: append at max+1024, head-insert at min−1024,
midpoint insertion with precision-exhaustion detection (nil on ties and
rounding onto an endpoint), renumbering to whole multiples of 1024, the
shared display-order tie-break (order, then folder name), and
tombstone-excluding overloads. 18 tests.
Claude-Session: https://claude.ai/code/session_018BjQRYBR6jQja3jCRi5S3A
