Wesrolter |
Any cuffs which limits arms movement should in theory work. They manifest their weapon by "grabbing" their mote, which floats near their head. So any cuffs which prevent them from raising their hands above their chest should do it, but the other suggestions of hand coverings would be a more secure method of doing it
Metaphysician |
Alternatively, you just manacle them, and if they manifest their solar blade, they still are in manacles. This should make them relatively easy to beat back into submission, because its not like the solar blade is a magic infinite cutting sword that would instantly slice through manacles. And if the Solarian can still beat you up despite having their hands shackled, well, you probably shouldn't have expected to keep them prisoner for long anyway.
Really, most forms of imprisonment should focus less on the logic of "disabling powers" and more on "responding to powers". You don't keep someone prisoner by keeping them helpless, you keep someone prisoner by being able to respond to bad behavior. Yes, this means CR 1 guards can't contain a CR 10 character if said character chooses otherwise, but this is system working as intended.