The master-file writer emits /entry/MX/indexedLatticeCount, but the
reader only looked for indexingLatticeCount (the name used by the
per-file MX plugin and data-file read path). Existing master files on
disk therefore returned no indexed-lattice-count vector. Read the
master's indexedLatticeCount first, falling back to indexingLatticeCount,
matching the niggli_class/niggliClass compatibility pattern. The writer
is left unchanged so already-written files keep working.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>