Are there two band contributions to diffusion current at the PN (diode) junction?
Are there two components of diffusion current (valence band AND conduction band) contributing to the generation of the PN junction voltage?

Yes

If so, do those components stay exclusively within their respective bands across the junction and throughout?

Electrons and holes that diffuse initially stay within their respective bands. Electrons in the conduction band and holes in the valence band. After enough time in the &quot;wrong&quot; band they will recombine with a carrier of the opposite type.

at the interface between the diode and the conductors attached to them, do valence and conduction bands both participate in electron current to and from their respective conductors since the valence and conduction bands of conductors overlap? Or is this pictured the ONLY transport to and from the semiconductors?

Electrons contribute to current in the conduction band and holes contribute to current in the valence band. Metals only have the conduction band available for use and can therefore only have electron current. At these metal-semiconductor junctions you therefore have electrons contributing to the current.
I don't really understand your diagrams, so I can't be sure about if they are right or not. I suggest drawing (or learning about) standard band diagrams instead. But, that being said, it looks like your first drawing depicts diffusion current as it initially occurs, and your second appears to depict recombination that will eventually occur. So, if that is what you intended, then the answer is: you get both.