Answers Lane F §8 (the counter is kind:'counter' in `places`) and closes the
keeper-spawn gap: buildInterior now returns room.counter = { mesh, pose, stand }
and tags the counter interactable with userData.keeperStand. `stand` = {x,z,ry}
where a shopkeeper stands (service side, facing the customer), in room-local
space, rig-front = local -Z per keepers.js. Deterministic; purely additive.
Verified in-browser: 36-build type sweep + 50-room soak — stand in-bounds,
faces customer (dot>0 all), carried on `places` (deep-equal), deterministic;
no change to existing placement, path, leaks, or perf (avg 3.6ms / worst 7.7ms,
geo/tex leak 0).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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