Issue 218: a mesh seat is answered by a module on a machine that does not hold it

2026-10-03 23:25:17 +02:00
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+---
+status: open
+opened: 2026-10-03
+located-in: []
+fixed-by:
+amended-design:
+---
+
+# 218 — A seat held once for the mesh is answered by a module on a machine that does not hold it
+
+## What was observed
+
+2026-10-03. Asked which databases the mesh's store holds, `mesh-store.databases` answered from the
+postgres on one machine with that machine's application databases; the controller's own database
+lives on the postgres of the other machine, which the controller's records name as the seat's one
+holder:
+
+```
+mesh-store  scope: mesh  delivers: postgres-database  holders: [ {node: <the control machine>, module: postgres} ]
+```
+
+The discovery console, which reads what answers on the bus ([ADR 0197](../../02-DECISIONS/0197-every-tool-announces-itself-on-the-bus-in-the-nats-services-protocol.md)),
+shows the same seat announced from **both** machines running postgres.
+
+## Why it matters beyond this instance
+
+A seat held once for the mesh promises one answerer: the role's holder. A module that implements a
+seat's verbs on every machine it runs on, and is let serve them on each, turns "the mesh's store" into
+"whichever postgres replied first" — a read against the wrong database that looks like a right one,
+and a write would be worse. Every mesh-scoped seat whose implementing module runs on more than one
+machine has this shape.
+
+## Where to look
+
+Whether the runtime serves a seat's verbs where its module merely *claims* the seat rather than where
+the mesh made it the holder ([ADR 0159](../../02-DECISIONS/0159-a-tool-call-names-the-machine-and-a-holder-serves-its-seats-verbs.md),
+[ADR 0160](../../02-DECISIONS/0160-the-mesh-issues-an-assignments-subjects-and-a-runtime-serves-what-it-is-issued.md)):
+the membership the controller issues each assignment, and what the runtime admits from it. A check:
+a mesh-scoped seat's verbs are served by exactly the holder the records name, on every machine.