Merge pull request 'Issue 087 is resolved: the mesh knows which host runs a machine' (#203) from issue/087-the-mesh-knows-which-host-runs-a-machine into main

2026-09-30 06:55:05 +00:00
parent 3ea9601904 0a5006b366
commit c2cf0d72d6
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.