tid_cloud_fill

Bakes the TIDES squall into the part's 3D density+colour volume, one voxel per invocation, every frame.

The field is authored at real scale: the volume spans roughly 9.6 km across and reaches from 350 m to 4500 m, so cloudBase and cloudTop in metres from preseed.tides.state mean what they say and the deck is genuinely far away rather than a low dome pretending to be sky.

Four things are layered into it:

• A squall line. A front advances along the wind axis. Ahead of it, thin scattered fair-weather cumulus at the high base; behind it, full coverage and towering congestus. At t = 0 the front is astern with open sky toward the sun; by t ≈ 24 it has swept past the whole visible box.
• The shelf. A hard-edged low band riding just above the cloud base behind the front. This is what takes the sun at t = 25 and what reads as "a black shelf" in the last beat.
• The slot. A narrow ragged wedge carved toward the sun's bearing, low in the sky and far out, opened only for bar 22 (t 26.25–27.5). It is what lets one hard shaft back through.
• The rain veil. Below the base, the shelf density in the same column is dragged downward as virga, scaled by rain01. Real volumetric medium, so it hangs where the cloud actually is instead of being a screen-space wash.

Lighting is three density taps toward the sun — 260 m, 700 m and 1500 m — giving transmittance exp(-occ), which is what produces the lit-rim / dark-core read that makes cumulus look like cumulus. Colours come from State.palette(t) (cloudLit / cloudShadow); the sun direction is read live from the scene so the clouds, the shadows and the glitter track cannot disagree.

Bindings are generated from bindings.yaml. The uniform run is 48 f32 (192 bytes) packed by preseed.tides.sky; the layout is documented at the top of shader.wgsl and both sides must be edited together.