rayferric/optifine-shaders ? reverse-engineered prompt

Build me a Minecraft OptiFine shader pack from scratch that aims for a realistic physically based look, but still works with normal vanilla style worlds and LabPBR resource packs. I want nice lighting, colored and softer shadows, screen space reflections, ambient occlusion, automatic eye exposure, atmospheric fog, and a procedural sky with good day and night transitions.

It does not need to be perfect or production ready yet, but it should feel like a real in progress shader pack with the main effects working and the code organized so it can be improved later. Please include support for giving vanilla textures believable fake PBR values where needed, and try to avoid the most obvious visual artifacts where possible.

If there are rough edges, that is fine, just keep them reasonable and note what is still unfinished, like water fog, waving water or foliage, bloom, clouds, motion blur, depth of field, and dimension specific tweaks. You can check current OptiFine shader docs online if needed.