gs_water

The standing water on the salt pan, as one engine-lit surface() shader with no texture slots.

It gives the sheet three things the greybox tint could not: a chop normal built from six travelling waves and a field of expanding rain-impact rings; a Beer-Lambert read of whatever the depth buffer says stands under it, bent by the chop's own slope, so the crust and the runway paint show through shallow water and fade out as it deepens; and an analytic sky evaluated along the reflected ray — horizon-to-zenith gradient, storm-deck lid, discharge lift, sun disc and glare, and the 41-degree primary / 52-degree secondary bands of the rainbow — written into emissive behind a Schlick Fresnel, because this world carries no reflection probe and the PBR environment term is black without one.

Every one of those sky terms is a material property. greensky/pan/water writes them each frame from the same palette the sky slice hands the cloud preset, so the water holds the sky the film is showing at that instant rather than a baked one. Consumed by gs_water.material, which pan_flood and pan_flood_far carry.