d2b9eb4870
First function-level package of Piece 2. v2Frame(command, payload) builds one v2 frame:
0x00 + be32(len(netstring)) + netstring(command 0x00 payload). Byte-exact tests (cat/hi, empty
payload nil==[]byte{}, binary payload riding untouched). @testdesigner proved satisfiability in
scratch + caught a be32 arithmetic error in the spec; @godev (deepseek default) implemented it —
the small-package decomposition carrying on the room grinder where the monolithic parser could not.