pub const PROTOCOL: u32 = 2;Expand description
Wire-protocol version a provider must echo before receiving work.
A provider built against a different schema is refused at the handshake rather than discovered through a verdict that means something else than it appears to.
Version 2 added Job::directory. That is why the number moved for
what looks like an additive field: a version-1 helper does not know
the key, so it runs the job in whatever directory it happens to be
in and returns a verdict that is well-formed, index-aligned, and
about the wrong tree. The handshake exists for exactly the changes
a silent default would survive.