The new default's whole claim is that a launcher configuring nothing still
finds a person's presets, and nothing asserted it through a real composition —
`user-root.spec.ts` plugs the service directly, and every other lane pins
`includeUserRoot: false` so the machine's home cannot decide a golden.
This lane boots the real base and web-app bundles with only the shipped root
patched in, points `$DSH_HOME` at a temp home before boot (the derived root is
resolved when the plugin is constructed), and asserts a preset placed there is
listed as `user`, reported healthy, authorable, and mountable into an agent
whose tool catalog it decides.