CANs note-existence handler should listen for SCRATCHFILE_ADDRESSED

So CAN can learn if the scratchfile contains a new note. The note-existence handler should listen to the SCRATCHFILE_ADDRESSED event. Once recieved, the handler should check if a note at this address exists in the notebook. CAN's note-existence handler should fire NOTE_EXISTENCE when it determines if a note exists.

Backlinks

• When a CAN scratchfile is addressed, check to see if the note is new
  • CANs note-existence handler should listen for SCRATCHFILE_ADDRESSED and emit NOTE_EXISTENCE. CAN's store should listen to SCRATCHFILE_ADDRESSED and NOTE_EXISTENCE