Chevrons no longer need to be built out of a special block - the plugin
picks gate.chevron-count frame blocks evenly spaced around the scanned
ring and remembers their resting material, so a chevron can rest as
plain obsidian (matching the rest of the frame) and only reveal itself
by swapping to gate.chevron-lit-material while dialing/open. Restoring
on close now puts back the original block instead of a fixed material,
so alternating decorative frames (e.g. obsidian/gilded blackstone) are
preserved exactly.