mat3_normalized_to_quat_fast
I think it is better to create the subpass and return a pointer (or nullptr if nothing to draw). It is clearer what is the inputs and outputs.
Move view_z_to_volume_z
& volume_z_to_view_z
to shader shared file as the Bound box init use it.
Document functions that returns bool. Even more so when the function name is not explict.
The viewport size should not be used as dimensions. Always use the render buffer size like light / shadow / motion blur do.
Use default world material for clearing instead of dedicated shader. The default output should be 100% transmission.
Frostbite approach is too generic. Provide exact source title and like to the presentatino/ paper.
Document functions that returns bool. Even more so when the function name is not explict.