mesh-build-go publishes the build runner as its own package, so the other build modules share it without mesh-sdk (ADR 0593 §1)

The runner, the toolchain guard, the fetch, the parsers, buildcpu, the conformance kit and mesh-pack move from mesh-sdk's
buildstep into modules/mesh-build-go/buildstep (own go.mod). mesh-build-go, mesh-build-node and mesh-build-image require it
by a same-repository replace; what the delivery parts read (the failure contract, the fetch request, the stale sweep, the
module tree shape, NewID, CapacitySetting) stays imported from mesh-sdk as sdkstep.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

modules/mesh-build-node/go.mod

@@ -3,6 +3,7 @@ module meshbuildnode
 go 1.26.0
 
 require (
+	git.novox.be/novox/mesh-catalog/modules/mesh-build-go/buildstep v0.0.0
 	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261102112556-abf5eace7791
 	github.com/distribution/distribution/v3 v3.1.2
 	github.com/nats-io/nats.go v1.54.0
@@ -80,3 +81,5 @@ require (
 	google.golang.org/grpc v1.83.2 // indirect
 	google.golang.org/protobuf v1.36.11 // indirect
 )
+
+replace git.novox.be/novox/mesh-catalog/modules/mesh-build-go/buildstep => ../mesh-build-go/buildstep