instead of 404, show persistent notification: space is private

x cancel

sign in to request/ask for access/invite

after sign in user needs to refresh?

request access

sends email to owner, x (blah@blah.com) wants access, [approve]?

server msg, x blah@blah.com can now access your space. go to space [share] to edit collaborators space link

sends email to collab

or client page w success notification is probably better