When a CAN scratchfile is addressed, check to see if the note is new

This helps CAN decide what to tell the user; and how commands should respond based on context. CAN should have a single state store which can be queried about the latest state of the scratchfile. Commands won't be able to respond to CAN events so state becomes necessary at this point.

CANs note-existence handler should listen for SCRATCHFILE_ADDRESSED and emit NOTE_EXISTENCE. CAN's store should listen to SCRATCHFILE_ADDRESSED and NOTE_EXISTENCE

Backlinks

• CAN's add command should save the current scratchfile as a note.
  • CAN's add command is intended to add new notes to the notebook. When a new note has been detected and the add command is run, this new note should be created at the correct address. Each address in a CAN notebook is a directory. Each CAN address contains the AST of the note at this address and a metadata file containing names.