Vision principle 2 extended: server = door for vanilla clients (vanilla
in, family out; primary current purpose git), client = door to vanilla
servers (family in, vanilla out — reverse-runner hub dials vanilla
sshd; runner stays vanilla by design). Type symmetry at the seam
(family-protocol types both directions, russh the vanilla side); honest
asymmetry recorded (server serves seam entries, client consumes family
types)