Approve 0057-0059, with four corrections from review

Not approved as drafted -- four things came out of checking them against each
other, and one was a bug that would have broken every upgrade.

The bug: 0059 specified Restart=on-failure while 0057 has the host restart onto
a new binary by exiting CLEANLY. on-failure does not restart a process that
exited zero, so every upgraded node would have been left stopped, having
successfully upgraded. Found by reading the two records against each other
rather than by either alone. Now Restart=always in all three places that
mention it.

The host cannot run in a container, and the reason is decisive rather than
stylistic: step 0 of the substrate bootstrap installs the container runtime, so
a host inside a container would need the thing it exists to install. It would
also break 0041 -- copy it onto a machine and run it stops being true when the
machine must already have a runtime. Everything above tier 0 is a container;
the host is not. That split is the tier boundary, not an inconsistency.

systemd is named rather than abstracted. An init is not a dependency in 0041's
sense: 0041 is about what must be installed before the host works, and an init
is not installed, it is what the machine already is. The unit file is the only
systemd-specific artefact and it belongs to the package, so a machine with a
different supervisor ships a different package.

The mesh is a watchdog, and my first draft was half an answer. Recovery must be
local -- nothing dials a node, and a host that cannot start cannot report. But
detection is the mesh's, and a local supervisor structurally cannot do it: it
sees one process failing and cannot tell a broken machine from a broken
release. Only something watching every node can, and that distinction decides
whether the response is "fix this machine" or "stop shipping this version". So
a host rollout is staged -- a few nodes, wait for heartbeats, continue or stop
on silence. Local rollback still needed, because the canary nodes break and
because a node offline during the rollout gets the declaration later with no
batch around it.

The first declaration is the overlay and nothing else. Forced, because a node's
address and peers are assigned rather than chosen. But also the way back in: a
node reachable over the overlay can be fixed by hand if a later declaration
breaks it, and a large first declaration risks a node that is broken and
unreachable at once.

Also stated plainly, because it reads as a contradiction: nodes reach each
other over the overlay and every node consumes from the broker; what 0039
forbids is an inbound CONTROL surface, not reachability.

And in 06: no node holds a credential to any control-plane store, for reads or
writes. Four ADRs already say this separately and none of them said it in one
place. Nodes state over the broker; the owning context writes. With a note that
most high-frequency writes are observability's, not the registry's -- routing
logs into the registry would be the shared-schema mistake arriving through a
door marked performance.

03-DESIGN/01-to-be/05-the-node-host.md

@@ -12,6 +12,8 @@ decisions:
   - 02-DECISIONS/0008-a-failed-step-fails-the-job.md
   - 02-DECISIONS/0041-the-host-depends-on-nothing.md
   - 02-DECISIONS/0043-a-declaration-is-an-ordered-list-of-owned-resources.md
+  - 02-DECISIONS/0057-the-host-is-a-root-service-installed-as-a-package.md
+  - 02-DECISIONS/0059-a-host-that-cannot-start-rolls-itself-back.md
 ---
 
 # The node host
@@ -115,10 +117,7 @@ the link; never asked downward.
 
 ## The process
 
-> **Proposed, not yet decided** —
-> [ADR 0057](../../02-DECISIONS/0057-the-host-is-a-root-service-installed-as-a-package.md) is
-> awaiting review. This section is written against it and moves into the document's `decisions:`
-> when the record is accepted.
+[ADR 0057](../../02-DECISIONS/0057-the-host-is-a-root-service-installed-as-a-package.md).
 
 **One `root` service on every node, plus command-line entry points for a person.** A machine
 without one is not a node ([ADR 0036](../../02-DECISIONS/0036-a-node-is-a-managed-machine.md)) —
@@ -167,12 +166,20 @@ Type=notify
 ExecStart=/usr/bin/nox-mesh-host run
 Restart=always
 RestartSec=5s
+StartLimitBurst=3
+StartLimitIntervalSec=120
 StateDirectory=mesh-host
 
 [Install]
 WantedBy=multi-user.target
 ```
 
+**`Restart=always` and not `on-failure`**: the host restarts onto a new binary by exiting
+*cleanly*, and `on-failure` would not restart it — an upgraded node would be left stopped,
+having successfully upgraded. The start limit is what
+[ADR 0059](../../02-DECISIONS/0059-a-host-that-cannot-start-rolls-itself-back.md) uses to decide
+a binary is broken rather than unlucky.
+
 **The package owns this file. The host never does.** It manages `service` resources, and its own
 unit is a service — the temptation is obvious and it ends with a host stopping itself half way
 through an apply, leaving a machine with nothing running to fix it. A declaration naming the