The vehicles are rows of a ludic.base Table with kind and owner as columns, every player's own by
an owner index and a nid map: vehicle_of walks only that player's rows, vehicle_by_nid is a map
lookup, and a player who leaves has their rows removed instead of the whole list rebuilt. ve_add
takes the owner, so the owner is filed once and never assigned around the table. Positions stay
on the record: a boat moves every frame and there are at most two a player. vehicles_test holds
the table (9 tests); the game builds against it and lab/unit passes (88 tests).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
