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+---
+status: located
+opened: 2026-09-29
+located-in:
+  - mesh-host internal/upgrade
+  - mesh-host cmd/mesh-host
+  - mesh-controller (no build source for the host; no resource delivers it)
+fixed-by:
+amended-design:
+---
+
+# 142 — The host is the one thing the mesh does not deliver
+
+## What was observed
+
+A change to the host was merged and could not reach any machine without a person copying a file.
+
+Checked on the mesh of four machines, 2026-09-29:
+
+- **The host is not a build target.** Asked what had been built for it, the control plane answered
+  `nothing has been built for mesh-host`. A merge on the forge builds every changed module and the
+  control plane itself, because the control plane is a module. The host is not one, and nothing
+  builds it.
+- **No declaration delivers it.** No resource kind names an executable to place on a machine, and
+  nothing on a machine fetches one.
+- **The half that recovers from a bad host exists and is unused.** `internal/upgrade` can report that
+  the executable this process started from has been replaced on disk, and records which version last
+  completed a reconcile so a shell script can roll back a host that will not start. The launcher reads
+  that record and rolls back. But `Replaced()` is called by nothing except its own tests — the
+  recovery is wired and the delivery was never built.
+- **Every machine runs a byte-identical binary, stamped by hand.** All four carry the same size and
+  the same timestamp, from the last time somebody built it on a workstation and copied it out. No
+  package owns the file.
+
+## Why it matters beyond this instance
+
+**The component that implements updating is the one thing not updated.** The mesh's stated shape is
+that a push produces the right builds and they reach the machines running them with nobody asking. It
+is true of every module and of the control plane. It is false for the host, which is what applies all
+of them.
+
+**It is a bootstrap problem being answered by a person.** The host cannot be an ordinary module
+because the host is what applies modules; a module that replaces the thing applying it has to survive
+its own replacement. That is a real difficulty, and the work already done — noticing that the
+executable changed, recording a known-good version, a launcher that rolls back — is the hard half of
+solving it. What is missing is the easy half, and its absence makes the hard half dead code.
+
+**A hand-copied binary has no record anywhere.** Nothing says which version a machine runs, so
+nothing can say a machine is behind, and the mesh's own account of itself — every machine current with
+its source — cannot include the host. Four machines agreeing today is luck, not a property.
+
+**And it silently gates any change that starts in the host.** A change that needs the host to report
+something new cannot be rolled out by merging it: the control plane must wait for a person, and until
+then it either refuses what depends on the new report or renders something wrong. That cost is paid by
+every future change of this shape, and it was paid today.
+
+## Open questions
+
+- How is the host delivered without being applied by itself? A candidate shape: the host is built like
+  anything else, published as an artifact, and the *running* host fetches and stages the next one, then
+  stands aside — which is what `Replaced()` was written for and what the launcher's rollback already
+  covers.
+- **Should this ride the bus, rather than becoming a mechanism of its own?** Everything else that
+  reaches a machine already does: a declaration is sent over it, a report comes back over it, and a
+  build announces what it produced on it, which is how a module's new version reaches the machines
+  running it. A host build announcing itself the same way, consumed by the host already running,
+  would make this the existing mechanism pointed at one more artifact rather than a second way of
+  delivering things. It would also give the machine somewhere to say which host it is running, on the
+  report it already sends.
+- What records which version of the host a machine runs, so "behind" is answerable? Nothing does now.
+- Does the host's version belong in its report, beside the other facts a machine states about itself?
+- Who decides when a machine takes a new host — the mesh, on a build, or an operator per machine as
+  with converging? The rollback path means a bad host costs a reconcile rather than a machine, which
+  argues for the former.
+- Does the same gap apply to the launcher and the units beside the binary, which are also files no
+  declaration names?