Issue 087 is resolved: the mesh knows which host runs a machine

The machine has reported its host version since ADR 0141, whose own comment says why it must: without it nothing can say a machine is behind. The controller's copy of the report did not have the field, so it unmarshalled into nothing and was thrown away on arrival. Two structs describe one message and only the sending side had it. node show names it per machine, "not reported" where the mesh has not been told. status names every machine running an older host than another does, and which is newest. Disagreement rather than staleness, deliberately: nothing delivers a host version yet, so the mesh holds no canonical current one and "behind" has no fixed point. What it can say is that the oldest host in the mesh is what the mesh may send. Two refusals to guess: a machine that reported nothing is not called behind, and versions compare as strings — right for the timestamps this mesh uses, wrong for a scheme where 10 sorts before 9, said at the place that would have to learn. 107 gains the note that this is what makes its new field safe to consider, and that one machine of four is behind today, so it is not free yet.
2026-09-30 08:54:52 +02:00
parent 3ea9601904
commit 0a5006b366
3 changed files with 84 additions and 3 deletions
@@ -1,8 +1,8 @@
 ---
-status: open
+status: resolved
 opened: 2026-09-22
-located-in: []
-fixed-by:
+located-in: [mesh-controller internal/link/protocol.go (the report field that was missing), internal/inventory, cmd/mesh-controller (node show and status)]
+fixed-by: mesh-controller 7683ba8
 amended-design:
 ---

@@ -0,0 +1,68 @@
+# 087 — resolved: the mesh knows which host runs a machine
+
+*2026-09-30.*
+
+## The field existed and was thrown away on arrival
+
+The machine has reported its host version since
+[ADR 0141](../../02-DECISIONS/0141-the-host-delivers-its-own-successor.md) — `Host` on the report, with
+a comment saying why it must be there: *"without it nothing can say a machine is behind."*
+
+**The controller's own copy of the report did not have the field.** Two structs describe one message,
+one on each side of the wire, and only the sending side had it — so it unmarshalled into nothing and the
+mesh could not answer a question the machine had been answering for a week. That is the whole of this
+issue's mechanism, and it is worth stating plainly because neither side was wrong on its own.
+
+## What it says now
+
+`node show` names it per machine:
+
+```
+  last heard from   here
+  host              2026-09-30-0214
+```
+
+`not reported — this machine has not said since the mesh began keeping it` where the mesh has not been
+told, because a machine that has not said is a different thing from a machine running nothing.
+
+`status` names the machines that are behind another:
+
+```
+1 machine(s) run an older host than another machine does:
+  ace          2026-09-29-0113
+
+  the newest any machine reports is 2026-09-30-0214. A host refuses a declaration carrying a
+  field it does not know, whole — so a new field reaches these machines last
+```
+
+## Disagreement, not staleness, and that is deliberate
+
+The open questions asked whether the controller should refuse to send a declaration a node cannot
+parse. It cannot yet, honestly: **nothing delivers a host version** (ADR 0141 is accepted and not
+built, which is [issue 142](../142-the-host-is-the-one-thing-the-mesh-does-not-deliver/00-report.md)),
+so the mesh holds no canonical current version and "behind" has no fixed point to be behind.
+
+What it can say truthfully is that these machines do not all run the same host, and which is newest of
+the ones it has been told about. That is the fact that matters before a declaration gains a field: **the
+oldest host in the mesh is what the mesh may send.**
+
+Two deliberate refusals to guess:
+
+- **A machine that has reported nothing is not called behind.** It may be running anything. `node show`
+  says it has not said, per machine, which is the honest form.
+- **Versions compare as strings.** That suits the timestamps and commits this mesh uses and is wrong
+  for a scheme where `10` sorts before `9`. Said in the code at the place that would have to learn,
+  rather than left as a surprise.
+
+## The open questions, answered as far as they can be
+
+- *Should a node report the version of its host?* It already did. The gap was the reading.
+- *Should the mesh refuse to send a field no node understands yet, or refuse per node and say so?*
+  Neither, yet — refusing needs the mesh to know which fields need which version, which is the third
+  question below and is not answered here. What it does is make the disagreement visible before
+  somebody adds a field.
+- *Is there a general shape — a declaration saying which version of the host it needs?* Still open, and
+  now cheaper to answer: the versions are recorded, so a minimum-version field on a declaration has
+  something to compare against. It belongs with
+  [issue 107](../107-a-declaration-carries-no-order/00-report.md), which wants to add a field and is the
+  first thing this makes safe.
@@ -40,3 +40,16 @@ exists there and is thrown away at the wire.
  separate genesis-digest branch is needed on the host?
 - Is a sequence enough, or does a mode change deserve its own marker, so a replayed converged
  declaration is refused by mode as well as by order?
+
+## What has since made this safer to do (2026-09-30)
+
+Adding a `sequence` to a declaration is adding a field, and a host refuses a declaration carrying a
+field it does not know — whole. That was
+[issue 087](../087-the-controller-cannot-tell-a-host-is-too-old/00-report.md), and it is resolved: the
+mesh now records which host each machine reports and `status` names every machine running an older one
+than another does.
+
+So the flag day is visible before it is walked into, which it was not when this was filed. It does not
+make the field free: **the oldest host in the mesh is still what the mesh may send**, and one machine of
+four is behind today. A sequence that an old host refuses takes that machine out of the mesh's reach
+entirely — worse than the replay it prevents, which has never been observed.