go

The Go toolchain as a module (novox/hq ADR 0477 §4, issue 1573).

Owns the package go. No other module declares it (checks/toolchains refuses one that does).
Provides go-toolchain with the machine's reach: dev-tools, lab and mesh-build-go require it, and the requirement is met only by this module on the same machine. It is never pulled in for whatever asked, so go is assigned to a node on purpose, and a node without it refuses a module that needs it at resolution.
Holds no long-running resource, so it adds nothing to health-undeclared.

The node-engine never uninstalls a package, so moving the declaration here removes nothing from a node.