Pass kinds:
image Exactly one final Image pass is required.
buffer Offscreen 2D pass. May be consumed by later passes and/or itself.
cubemap Cubemap pass.
Each pass points at one GLSL file with a ShaderToy-style mainImage/mainCubemap
entry point.
Inspect one pass:
shadertoy inspect pass buffer-a
shadertoy render --pass buffer-a -o target/buffer-a.png