One skate3rust process validates TEST_WORLD and every converted map over
stdin/stdout (SKATE_MAP_CHECK lines). Existing checks still fail a map;
new spawn-support / neutral-startup / invisible-collision checks report
warnings. Setup falls back to per-map --check-assets with an older exe.
See docs/hails-additions/06-map-validator.md (PR F).
Note: install.py also carries PR G's customiser-overlap hunks
(available_memory, overlap_customiser, Background); they are interleaved
with the validator wiring in _install and are documented in doc 08.
