I need some answers.
Please elaborate, this is a new technology and no one really know how byteball DAG works.
1) Who responsible for hardforks? Should witnesses vote on hardfork? Or it's only depends on developers and right repository?
2) Is there a way to prune old transactions from local database and build transactions on some fresh ones? Is it necessary to keep all DAG on a disk?
3) Is there a SPV wallet? Is it possible to make SPV wallet?
4) Why 12 witnesses, not 1200? From technical point of view, not politics. Is every transaction should carry all witnesses list with it? So transactions will be bigger proportionally to list of witnesses? Or not, and there is no problem to do 1200, 12000 or 1200000 witnesses potentially?
5) Can witnesses change max supply of coins and generate 10000 tb more? If not, who can?
1) Hardforks are inbuilt into DAG, kind of, depends on what you mean. See in Byteball, despite CfBs lies, and unlike Ethereum its possible to grow many "histories" many "chains" at the same time, on different nodes, and these will be part of the Main Chain - ordered according to when they are seen, and they will be included if they do not double-spend. Who decides this ordering and following of "do not double-spend"? Who "sees"? Witnesses! They only see transactions and post their own approvals, stamps.
2) A very efficient and secure Light Client exists. You can keep the DAG in memory today, is only 1.4GB, there is no pruning done, yet storage efficiency can be improved later.
3) Yes, very light, Android app is such by default.
4) 12 is a good selection, too many like 1200 would be difficult for humans to know and replace/talk-about, too little would be easy to collude together. This is one of the few "chosen by gut instincts" variables/constants in Byteball. Yes tx carry witness list, all 12, but can be smaller for efficiency in a witness_list_unit, when the same list is known previously, thus re-shared.
5) There is no proof-of-work and no generation of coins, all are existing and generated in genesis unit, form which distributions take place every full moon.