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+---
+status: open
+opened: 2026-09-22
+located-in: []
+fixed-by:
+amended-design:
+---
+
+# 087 — The controller cannot tell that a node's host is too old for what it sends
+
+## What was observed
+
+Found in review of the adoption-mode build, 2026-09-22, by reading the code.
+
+A host parses a declaration strictly: a field it does not know makes it refuse the whole
+declaration, and nothing is applied. That is deliberate, and it is what keeps a half-understood
+declaration off a machine. It also means every new field in a declaration is a flag day: hosts
+must be upgraded before the controller sends it.
+
+The controller has no record of which version of the host a node runs. It is not in what a node
+reports, and it is not in the node's profile. So when a node refuses a declaration for that
+reason, the mesh shows the node failing and relays the host's refusal. Nothing says *the host on
+this machine is older than what the mesh now sends*, and nothing could have said so beforehand.
+
+Adoption mode adds four such fields, one of them on the declaration of **every** node, and its
+merge order exists for this reason alone: the host merges first, every machine is upgraded, then
+the controller.
+
+## Why it matters beyond this instance
+
+Every future field in a declaration has the same flag day, and the mesh upgrades itself. A mesh
+that cannot say which machines are ready for what it is about to send has to be upgraded by
+someone remembering the order. The rule that a host refuses what it does not understand is right;
+the missing half is that the controller should know before it sends.
+
+## Open questions
+
+- Should a node report the version of its host, so the controller can refuse to send a
+  declaration a node cannot parse, and say which machines are behind?
+- Should the mesh refuse to send a field no node understands yet, or refuse per node and say so?
+- Is there a general shape here — a declaration saying which version of the host it needs — or is
+  a reported version enough?