A definition names no installation: the check, an operator's value, a context on the git seat

InstallationProblems judges every value the mesh acts on for a name under a public top-level domain
or a public address, with prose, the world's registries, resolvers and certificate authorities
exempt, and a name a resource means on purpose declared with its reason (names-on-purpose). Run by
module check and a catalogue-wide test, not yet at registration, while the declared list shrinks.
${setting:<key>} fills a file from the assignment's settings and is refused when nothing set it.
A build context may live on the git seat; the request carries the seat's clone base (novox/hq ADR
0112, ADR 0155, issues 122 and 134).

internal/catalogue/manifest.go

@@ -549,8 +549,14 @@ type BuildsOn struct {
 type ArtifactContext struct {
 	// Repository is cloned fresh, the same way the module's own repository is — a working tree
 	// nothing has touched, so what was built is reproducible from the two commits named rather
-	// than from whatever a previous build happened to leave behind.
+	// than from whatever a previous build happened to leave behind. A URL, or — with Seat — a
+	// path on that seat's holder, `<owner>/<name>`.
 	Repository string `json:"repository"`
+	// Seat is the seat the repository lives on: `git` for this mesh's own forge (novox/hq ADR 0111,
+	// ADR 0155). A context written as a URL names one installation's forge and can be built
+	// nowhere else; a path on the seat is composed by the mesh that builds it, whichever forge
+	// holds the seat there.
+	Seat string `json:"seat,omitempty"`
 	// Ref is the branch, tag or commit of that repository to build. Empty means its own default
 	// branch — the same meaning an empty module ref already has.
 	Ref string `json:"ref,omitempty"`