---
layer: to-be
status: in-progress
code:
  - mesh-controller internal/catalogue/seats.go
  - mesh-controller internal/catalogue/resolve.go
  - mesh-controller cmd/mesh-controller/seats.go
  - mesh-controller cmd/mesh-controller/source.go
  - mesh-controller internal/inventory/migrations/0032-a-source-may-live-on-a-seat.sql
  - mesh-catalog modules/gitea/module.json
updated: 2026-09-25
decisions:
  - 02-DECISIONS/0110-a-seat-is-a-module-assignment-from-a-closed-set.md
  - 02-DECISIONS/0111-a-build-source-is-on-the-git-seat-or-external.md
  - 02-DECISIONS/0109-a-package-registry-seat-is-one-per-ecosystem.md
---

# 26 — The seats

**What a mesh can have one of, and who fills each.** A seat is a named role at a scope, taken by a
module assignment. The mesh defines which seats exist. Occupying one may deliver a provision, and the
list of seats with their holders is the quickest answer to "what is in this mesh".

## What a seat is

A seat has four properties, fixed by the mesh rather than by any module:

| property | is |
|---|---|
| name | what a manifest claims, and what a person reads in the list |
| scope | node, site or mesh: where its capacity applies. Every seat in the set has a capacity of one, so one holder per scope. A bench, a seat with several holders, is a word the glossary keeps and no seat uses yet |
| delivers | the provision its holder answers for, or nothing |
| decision | the record that made it a seat |

**A module assignment holds a seat by claiming it.** The claim is the manifest's `claims`, and it is
satisfied by assigning the module somewhere. The seat is not a second record beside the assignment.
It points at the assignment, and everything the mesh knows about the holder is what it knows about
that assignment: the node, the node's settings for the module, and what the module serves.

**The set is closed.** A claim naming a seat the mesh does not define is refused, and so is a claim at
the wrong scope. Adding a seat is a decision, recorded, for the reason every addition to the host's
vocabulary is one: the set is what a person reads to learn what a mesh can have, and an entry nobody
argued for is an entry nobody can explain.

## The set

| seat | scope | delivers | typically held by |
|---|---|---|---|
| `mesh-controller` | mesh | — | the controller |
| `mesh-store` | mesh | — | the foundation's store |
| `mesh-broker` | mesh | — | the foundation's broker |
| `mesh-vault` | mesh | `secret` | the vault |
| `the-artifact-store` | mesh | `artifact-store` | the artifact registry |
| `the-catalogue` | mesh | — | the catalogue |
| `npm-package-registry` | mesh | `npm-package-registry` | the forge |
| `git` | mesh | `git` | the forge |
| `the-build-machine` | node | — | a builder |
| `the-dns-port` | node | — | the local resolver |
| `the-intrusion-prevention` | node | — | an intrusion-prevention service |
| `the-packet-filter` | node | — | the packet filter |
| `the-private-network` | node | — | the private network the mesh runs over |
| `the-resolver-configuration` | node | — | whichever of the alternative resolver configurations is chosen |
| `the-showcase` | node | — | the showcase module |

The controller holds this set in code, and a test asserts both its size and that every entry names
the record that made it a seat. **This table and [ADR 0110](../../02-DECISIONS/0110-a-seat-is-a-module-assignment-from-a-closed-set.md)
govern, and code that disagrees is what is wrong.** The implementation in progress predates two
things here: the `mesh-vault` seat, and the rule that `mesh-store` and `mesh-broker` deliver
nothing. It is brought to this table before it merges.

## A seat that delivers a provision

A seat that delivers a provision may only be held by a module that provides it, at the seat's scope.
A mesh seat delivers a mesh-scoped provision.

**A seat delivers a provision only where the mesh has one answer for everyone.** The artifact store,
the npm registry, git and the vault are each one per mesh by decision. The store and the broker are
not: nodes run their own stores and a consumer uses the one on its machine
([23 — Choosing a provider](23-choosing-a-provider.md)). So their seats guard that the foundation's
own server is singular, and route nobody.

**Its holder answers for that provision.** A requirement for it resolves, in order, to:

1. the provider the consumer's node was pinned to, because a consumer coupled to one provider's
   contents has said so ([23 — Choosing a provider](23-choosing-a-provider.md));
2. the holder of the seat, **even when another provider runs on the consumer's own machine**;
3. otherwise nothing, and the requirement is refused, naming the unheld seat.

Co-location, which answers first for every other provision, does not apply here: a seat says which
one is the mesh's, and co-location answering first would let any second provider on a consumer's
machine take over for that consumer, silently. So a second provider can run beside the holder and
harm nothing. The forge holds
`npm-package-registry`. An npm proxy may provide the same provision on another machine, and a module
requiring an npm registry is still served by the forge, without anybody pinning it.

**Moving the role is changing which module claims the seat, and today that is a definition change.**
A claim is part of a module's definition, so the proxy's definition must claim the seat and the
forge's must stop. The forge cannot simply be unassigned, because it holds `git` as well. Every
consumer follows once the claim moves. Making *which* seats a module holds the assignment's choice,
with the definition saying only which seats it *can* hold, is the consistent answer, and
[27 — A module requires, the mesh resolves](27-a-module-requires-the-mesh-resolves.md) lists it as
not yet settled.

**What a consumer receives is a grant**, the same as for any provision: where the provider answers,
what it serves, and a credential. A consumer never reads the seat directly. The one exception is the
controller itself, which reaches the store and the broker through a narrow seat placeholder,
because it made them before any module existed and cannot be their consumer. One foundation module
also reads it today, to find its own server's port. [27](27-a-module-requires-the-mesh-resolves.md)
moves that to a host port requirement.

## A seat that delivers nothing

Most node seats deliver nothing. They say which module is this machine's packet filter, or which of
two alternative resolver configurations it runs, and a second holder is refused. That is the whole of
their job, and it is a real one: it is the mesh saying what a machine is, in words a person can read.

## The overview

The controller lists every seat in the set with its scope, what it delivers, and each holder as a
node and a module. A seat nobody holds is listed as unheld. That is an answer, "this mesh has no
forge", and not a fault.

Holdings are derived from assignments whenever they are asked for, never stored. The list is always
what the mesh is running, because it is computed from the same thing that decides what the mesh runs.

## The git seat, and where a build comes from

A module is built from a repository, a path and a ref. The repository is one of two things, and the
mesh records which:

| form | means | recorded as |
|---|---|---|
| on the `git` seat | a repository on the forge that holds the seat | its path on the forge, and the seat |
| external | a repository anywhere else, a public forge for instance | its URL, exactly as given |

For a repository on the seat, the controller composes the clone URL at the moment of building,
from where the holder runs and the scheme and port it serves for `git`. The recorded source never
contains an address, so moving the forge changes nothing that was recorded. The build machine is not
told the difference: it receives a URL either way.

With the seat unheld, a build from the seat is refused and says why. External builds carry on.

**Not yet designed:** a credential for cloning a private repository. The mesh's own repositories are
public. The natural place for a clone credential is the `git` provision's grant, and that is a
decision still to take.