---
status: open
opened: 2026-09-17
located-in: [mesh-controller, mesh-host]
fixed-by:
amended-design:
---

# 056 — An adopted module assigned to a second node raises a second server

## Symptom

The store and broker are adopted in place ([ADR 0078](../../02-DECISIONS/0078-the-store-and-broker-are-modules.md),
issue 051): genesis raises `mesh-store`/`mesh-broker` on the control-node, and assigning the
`postgres`/`lavinmq` module there makes the module reconcile the already-running container instead
of raising a new one. Adoption works *because the container is already running on that node*.

Nothing stops the same module being assigned to a **second** node. On a node where no
`mesh-store` is running, the applier finds no container by that name and raises one — a second
postgres, a second broker. The whole point of Phase 3 — "one postgres, one lavinmq" — holds only
by the convention that genesis assigns these modules to the control-node alone; it is not enforced.

## Why it matters

"There is one store and one broker" is stated as a property of the mesh, and a property enforced by
nothing is indistinguishable from a wrong one. A single extra `assign` — the ordinary verb an
operator types — silently produces a divergent second server holding none of the first's data, and
consumers resolved to it get an empty store. The failure is silent and far from its cause.

The exclusive foundation modules are the mesh's clearest case of "there is one of me," yet unlike a
mesh-scoped seat, an adopted module carries no claim that the resolver would refuse a second holder
for.

## Open questions

- Should `postgres`/`lavinmq` claim a mesh-scoped exclusive seat (the way `mesh-controller` claims
  `the-controller`), so the resolver refuses a second assignment by the same mechanism that keeps
  one controller?
- Or should adoption be explicit — a module that adopts a foundation container declares it, and the
  controller refuses to place it on a node whose foundation did not raise that container?
- How is "one postgres, one lavinmq" checked, rather than assumed — in the resolver, in `status`, or
  in a bed that tries the second assignment and asserts the refusal?