- - i_resp_previously, previously should include which tags ?
- replay prevention all of them
- - rpush negotiation for which tag to sign
- - big comment in dgit-repos-server (search for `we are updating only')
- - dgit-repos-server readupdates tag regexp
- - test suite tests/lib
+ - protocol version 4
+ implies ability to sign new tag (this is already there
+ so simply advertising version 4 will work)
+ needs also new ability to sign old-format tag in split
+ brain way
+