Building tier 0 forced the question "the one binary installed by hand" had been
carrying unexamined. A TypeScript host needs a runtime present before it runs,
so the thing installed by hand becomes two — and the second must be installed by
the means the host exists to replace.
So the host is a statically linked binary that requires nothing present, written
in Go. Rejected: a runtime installed first, which breaks the property the tier
rests on; and bundling the runtime into the executable, which carries ninety
megabytes to preserve a language choice and puts a young feature at the bottom
of the stack.
The argument that decided it is architectural rather than about taste. 0037
means the host never queries the mesh database and 0039 means it only receives
declarations, so the host shares NO code with any other tier — not a client, not
a schema, not the SDK. The language boundary falls exactly on a boundary that
already exists, and a second language usually costs duplicated logic where here
there is none to duplicate.
§8 gains a scope: it said "TypeScript throughout" when everything was a service
or a surface, and is now scoped to those with tier 0 named. Another sync owed.
Playbook 04 steps 2 and 4: repos.md records mesh-host as existing, the design
takes code: [mesh-host] and status: in-progress.
