register Proof_Document instances as session entities -- handle Markup.EDIT messages locally;

tuned signature of isabelle.Position;

maintain generic session entities -- cover commands, states, etc. (but not yet documents);

unified Command and Command_State, eliminated separate Accumulator; Command.finish_static: idempotent transition from static to dynamic mode, taking snapshot of final state (which will never change later);

removed experimental history panel;

more explicit modeling of Command and Command_State as Session.Entity; misc tuning;

updated;

tuned;