I would like to copy the value from a selectable SAIL gridField into a rule inpu

As stated in the answer to your previous post the ri! namespace cannot be used as a target for saving a value. You need to have local!selectedDocumentId in the load() section of your expression and then in the with() section you can pass it into a rule:
load(local!selectedDocumentId,
with(
a!gridField(...),
local!exprResult: rule!myRule(local!selectedDocumentId)
))

There is no separate rule called myRule....I am using the selectedDocumentId inside of the same rule where I have all the grid functionality being written....and I want to pass the value of selectedDocumentId into a rule input ri!selectedDoc inside the same rule.....later I will pass this rule input into a pv variable which can be used inside a Delete Document smart service to delete that document using its id that was passed from local!selectedDocumentId to ri!selectedDoc to the pv! variable I declared.