pub const PROTOCOL_VERSION: u32 = 1;Expand description
What this build speaks.
The wire had no version at all, while the two other formats this
workspace persists — tracking records and experiment records — both
carry one. A driver and a worker from different builds simply
exchanged JSON and hoped: a field the receiver did not know was
dropped by #[serde(default)], so a plan compiled by a newer
coordinator ran with pieces of it silently missing, and the failure
surfaced as a wrong result rather than as a refusal.
Bump it whenever a change alters what a peer must understand to execute a plan correctly — not for a purely additive field that an older peer can safely ignore.