It's should be possible to go into air layer from visitable object (but opposite isn't allowed).
And when walking on water player can't really interact with any object at all so future movement always possible.
This way we can avoid layer checks when calculating paths by ignoring unitialized tiles entirely.
Also at this point pathfinder and movement actually works for everything except flying.
This still need investigation, but likely most of external code shouldn't be aware of layers in order to work properly because only LAND and SAIL can be targeted and single tile can't have both of these layers.
