Brush face texture x y scale (and potentially other data) should be exposed to shaders

Would it be possible to expose the brush face x y scale in the ShaderAPI or some other appropriate place? I'm working on a interior mapping shader where, to project a lightmap into a fake room, I need to calculate the direction vector in tangent space from a closest / strongest light origin to a projected pixel. I can calculate the vector from the light origin to a pixel on the surface of a brush and transform it into tangent space, but the vector from the texture corner to the pixel on the surface and from the texture corner to the projected pixel all have values between 0..1 as a fraction of the base texture. To convert these to hammer units, I can get the texture dimensions in the shader helper file and values of the $basetexturetransform material parameter, but the size of the texture also depends on the brush texture scale which is not available anywhere.

Another reason why exposing this would benefit the modding community, Tony Sergi was working on porting a goldsrc feature to the source engine, and could not proceed because this data isn't exposed.

Start by locating the ShaderAPI and the brush-face texture coordinate data involved in shader access. Investigate where brush texture scale is represented and how existing shader parameters are exposed. Done means an interior-mapping shader can access the brush face x/y scale, with the appropriate shader-facing behavior verified.