This may interest some people, it's a brief explanation of how I think outbox should work ideally (criticism and suggestions welcome):

nostr:nevent1qvzqqqqqqypzqwlsccluhy6xxsr6l9a9uhhxf75g85g8a709tprjcn4e42h053vaqyd8wumn8ghj7urewfsk66ty9enxjct5dfskvtnrdakj7qgmwaehxw309aex2mrp0yh8wetnw3jhymnzw33jucm0d5hszxnhwden5te0d3hkx6mzdauzuenfv96x5ctx9e3k7mf0qqsrj67sh8ag73wqapmle7yy5huqwr2hwx77wqz0x0cz94hqmd0f22cunkj50

You can't have this local database thing in all contexts like all microapps and whatnot (those can probably just use a naïve NIP-65 approach) but a full-fledged Nostr client should.