const NO_KERNEL_WATER: -1e+30
The water level the kernel writes where there is none, and packs for a
node under no lake: below any ground, so every comparison against it
reads "dry". The producer turns it back into the NaN Heightfield.water
carries, which WGSL cannot spell as a constant. It is NO_STANDING, so
a drowned reach's lane reads the same way.