The lease file is gone — builds coordinate through the mesh

After its first production run coordinated a full gated build cleanly, the build protocol is now the default on every deployment — no flag needed. The file lease that used to decide which server bakes is deleted outright: its one-builder guarantee and its "a dead builder is superseded automatically" property both live on in the build root's claim, where they are ordinary, observable mesh state instead of a hidden file on a shared volume.

Servers that are not building no longer poll the shared cache every minute to see whether the builder finished — they subscribe to the build's GO signal and complete the moment it lands.

The escape hatch remains for hosts with nothing to coordinate: switching the protocol off simply bakes solo, which is the right shape for a single-process setup and the wrong one for any fleet.