01fb2e13 named nats.go and its dependencies in checkermsg's go.mod but left the go.sum
lines uncommitted, so the fetch's proof (both build tags, GOPROXY=off) refuses the
module with "missing go.sum entry" on any clean clone.
Builds: design 47 G (the join's guard rule)
Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h