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jschoubben 7b4916e9ec Modules declare their own seats; the mesh reserves mesh-*

The architecture 0117 opened needs a module to offer a service as a role on
the bus — one holder, addressed by what it does. A closed table in the
controller cannot express that: a capability a module contributes would
require changing the mesh itself.

But 0110 closed the set for a good reason — nothing could say what seats a
mesh had, and the hand count came out at eleven of thirteen. That argues for
enumerable, not hardcoded, and 0110 weighed free-form against a fixed table
without considering a third option: closed at any moment and derived from
the catalogue. A derived list cannot drift, which is how the count broke.

So: the mesh's seats stay the mesh's, reserved by the mesh- prefix so the
prefix is the rule and there is no list to maintain; ten seats are renamed
to restore 0079's convention; everything 0110 decided about what a seat IS
survives untouched.

Design 29 carries the declaration model: three namespaces, subjects derived
from local names so a manifest survives the wire changing, queues never
declared, five relationships (the job and state shapes 0041 had no room
for), and the build-publish-deploy lifecycle with hard, soft and build-time
dependencies distinguished.

0041 gets a progressive insight: "no per-consumer setup, only a
subscription" was a fact about a topic exchange, and a JetStream durable
consumer is a real object someone creates.

WBS 1.3/1.4 were wrong and say so: streams come at registration and
consumers at assignment, so only the foundation set belongs at genesis.

2026-09-26 20:34:32 +02:00

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Glossary — the words this repository uses, and the ones it stopped using

One name per thing. This page is the authority; where an older record says something else, that record is being superseded, not this page. It exists because the terms kept drifting in conversation — control plane / controller / master / hub for one thing, substrate / foundation for another — and a mesh you cannot name precisely is a mesh two people describe differently.

The mesh and its machines

node — a machine in the mesh. There are 0..n of them, and each runs the host agent. A node is just a machine that has joined; being one implies nothing about what it runs.
control-node — the one node that also holds the mesh-controller seat. There is exactly one per mesh. "control-node" is not a separate kind of machine — it is a node that additionally runs the controller (and, today, the foundation). Lose it and the other nodes keep running what they were last told; they simply cannot be told anything new.
~~master / slave~~, ~~hub / peer~~ — not used. The relationship is controller and nodes, and no node is subordinate: a node applies declarations on its own and survives the control-node dying.

What runs the mesh

controller — the component that decides what each node should be, holds the mesh's records, and tells nodes over the broker. Replaces "control plane" (borrowed from networking's control-plane/data-plane, and opaque here).
mesh-controller — the module that runs the controller. It claims the mesh-controller seat at mesh scope, which is what makes it singular. Replaces the module name mesh-control. (The git repository has been renamed mesh-control -> mesh-controller on the forge; the module, container and image it produces are mesh-controller.)
foundation — the store and the broker, raised at genesis before any module system exists. Replaces "substrate" (a biology metaphor that landed for no one). The foundation is not a third thing beside the store and broker — it is those two, named together.
store — the one postgres server. It holds the controller's own context databases (inventory, identity, licences — a context owns its store, ADR 0008) and every module's own database. One server, many databases — never one shared "mesh database".
broker — the one lavinmq message bus. It carries the mesh bus on the / vhost and a vhost per consumer that requires amqp.

What the mesh stores and serves

package — what code resolves when it is compiled: an npm/cargo/pypi dependency, by version. Served by the package-registry (gitea). Only a builder talks to it.
artifact — what the mesh delivers to a machine to install and run: an OCI image, by digest. Served by the artifact-store (distribution). Every node pulls from it.
These are two protocols, not one store being weak — see ADR 0075.

How modules relate to the mesh

seat — a named role at a scope (node / site / mesh), held by a module assignment, from a closed set the mesh defines: a claim naming a seat outside the set is refused. A seat may deliver a provision, and its holder is then the mesh's answer for it when several modules provide it (ADR 0118 (superseding ADR 0110)). The set, with who holds each seat, is the overview of what a mesh has (26 — The seats). A seat has a capacity: a capacity-1 seat is exclusive (one holder); a higher-capacity seat is a bench (several holders coexist).
claim — a module taking a spot on a seat. claims: [{name, scope}] in a manifest. A mesh-scoped exclusive claim is how the mesh says "there is one of me". A foundation seat is named after the server it guards: the mesh-controller, postgres and lavinmq modules claim the mesh-controller, mesh-store and mesh-broker seats (ADR 0079).
provision — a service one module provides and others require; the mesh resolves a provider and wires the two with an endpoint and a credential. A provision is a service you offer, a seat is a role you occupy, and the two meet where a seat delivers a provision: occupying the seat is what makes a module the provider of it.

How this page is kept

A new name for an existing thing lands here first, in the same change that introduces it in code. A record under 02-DECISIONS/ keeps whatever word it was written with — those are immutable — so a term retired here may still appear there, and the mapping above is how to read it.

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