ADR 0110 and 0111: a seat is a module assignment from a closed set, and a build source may live on the git seat

Seats have been doing two jobs and neither is written down. The mechanism ADR 0009 introduced is
enforced — a second holder is refused — but any well-formed name becomes a seat by being claimed,
and nothing can say which seats a mesh has or who holds them: holdings are assembled while planning
and discarded. The enumeration done while preparing this missed the control plane's own manifest,
because core modules' manifests live in its repository rather than the catalogue.

0110 closes the set. Each seat has a name, a scope, what occupying it delivers, and the record that
made it one; a claim outside the set is refused. A seat is held by a module assignment, and what the
mesh knows about the holder is what it knows about that assignment — nothing is stored beside it. A
seat may deliver a provision, and then its holder answers for it among several providers: pin, then
the holder, then the only provider, then refused. That keeps 0009's "refused, never guessed": the
seat is the choice made once, mesh-wide, instead of a pin per consumer node. The first set is the
eleven seats already claimed plus 0109's npm-package-registry, so nothing in use is refused.

Two concepts — seats for exclusion, a new word for consumable singulars — was rejected: both mean
"this mesh's one X", and the overview a person wants is one list.

0111 gives the mesh a git seat and makes a build source one of two explicit forms: a repository on
the seat's holder, recorded by its path and cloned from wherever the holder runs at build time; or
an external URL, recorded and cloned exactly as given. Recognising self-hosted sources by matching
URLs against the forge's address was rejected — it fails in the one case it exists for, after the
forge moves. Credentials for private repositories are left undecided and said so.

Design: new to-be 26 (the seats); 23 gains the seat step in resolution; 18's source entry names
the two forms; the glossary's seat and provision entries say where they meet. 0109 is carried from
its own branch so every link here resolves.

00-META/glossary.md

@@ -44,15 +44,22 @@ another — and a mesh you cannot name precisely is a mesh two people describe d
 
 ## How modules relate to the mesh
 
-- **seat** — a named position at a scope (node / site / mesh) with a **capacity**. A capacity-1 seat
-  is exclusive (one holder); a higher-capacity seat is a **bench** (several holders coexist).
+- **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 0110](../02-DECISIONS/0110-a-seat-is-a-module-assignment-from-a-closed-set.md)).
+  The set, with who holds each seat, is the overview of what a mesh has
+  ([26 — The seats](../03-DESIGN/01-to-be/26-the-seats.md)). 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](../02-DECISIONS/0079-the-foundation-seats-are-named-after-their-servers.md)).
 - **provision** — a service one module `provides` and others `require`; the mesh resolves a provider
-  and wires the two with an endpoint and a credential. This is separate from seats: a provision is
-  a service you offer, a seat is a slot you occupy.
+  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