Ref T12616. Ref T8047. Ref T11093. We currently have several bugs where diff state sticks across Quicksand pages.
Add a new top-level object to handle this, with sleep() and wake() methods. In sleep(), future changes will remove/deacivate all the reticles/editors/etc.
See T12616 for high-level discussion of plans here.
This general idea is likely to become more formal eventually (e.g. for "sheets" or whatever we call them, in T10469) but I think this is probably a reasonable place to draw a line for now.