blank credentials by default are needed when:

 - when running offline/no reason/intention to sync
 - when syncing using a future tool (to be developed), that tool would run on :8332
   and serve blocks from the Bitcoin P2P network. That won't require the BTC RPC/server
   option, and by extension our config file won't be needed.

in any case new_miner_start() must go, even with blank credentials

the blank credentials cannot be entered into bitcoin's config file. that's exactly
what we need! the user who is capable to edit config files won't be able to do the
wrong thing but will instead be forced to set identical strong credentials in both files.

can't comment on merged main page non synced messages, I don't see the code.