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).

cmd/mesh-controller/source.go

@@ -82,6 +82,16 @@ func cloneFrom(ctx context.Context, source buildSource) (string, error) {
 // serves no scheme or port has nothing to compose from — a default port here would be the forge's
 // address guessed, which is the thing this exists to stop.
 func clonedFromSeat(world catalogue.World, seatName, repository string) (string, error) {
+	base, err := seatBase(world, seatName)
+	if err != nil {
+		return "", err
+	}
+	path := strings.TrimSuffix(strings.Trim(repository, "/"), ".git")
+	return fmt.Sprintf("%s/%s.git", base, path), nil
+}
+
+// seatBase is `scheme://host:port` of a seat's holder as the mesh reaches it, for cloning.
+func seatBase(world catalogue.World, seatName string) (string, error) {
 	seat, known := catalogue.SeatNamed(seatName)
 	if !known || seat.Delivers == "" {
 		return "", fmt.Errorf("%q is not a seat a repository can live on", seatName)
@@ -94,9 +104,9 @@ func clonedFromSeat(world catalogue.World, seatName, repository string) (string,
 		}
 	}
 	if holder == nil {
-		return "", fmt.Errorf("nobody holds the %s seat, so %s cannot be cloned from this mesh's "+
+		return "", fmt.Errorf("nobody holds the %s seat, so nothing can be cloned from this mesh's "+
 			"forge — assign a module that claims it, or build from the repository's URL without --self",
-			seat.Name, repository)
+			seat.Name)
 	}
 	var provider *catalogue.Provider
 	for i, p := range world.Offered[seat.Delivers] {
@@ -118,8 +128,33 @@ func clonedFromSeat(world catalogue.World, seatName, repository string) (string,
 		return "", fmt.Errorf("%s on %s holds the %s seat and does not serve a scheme and a port for %q",
 			holder.Module, holder.Node, seat.Name, seat.Delivers)
 	}
-	path := strings.TrimSuffix(strings.Trim(repository, "/"), ".git")
-	return fmt.Sprintf("%s://%s:%s/%s.git", scheme, provider.At, port, path), nil
+	return fmt.Sprintf("%s://%s:%s", scheme, provider.At, port), nil
+}
+
+// seatBases is the clone base of every seat a recipe's context may name, for a build request
+// (novox/hq ADR 0155). A seat nobody holds is left out rather than refused here: the build may not
+// name it at all, and if it does the builder refuses with the seat's name.
+func seatBases(ctx context.Context) map[string]string {
+	open, err := openStores(ctx)
+	if err != nil {
+		return nil
+	}
+	defer open.Close()
+	shelf, err := open.inventory.Catalogue(ctx)
+	if err != nil {
+		return nil
+	}
+	world, err := theRestOfTheMesh(ctx, open.inventory, shelf, "")
+	if err != nil {
+		return nil
+	}
+	bases := map[string]string{}
+	for _, seatName := range []string{gitSeat} {
+		if base, err := seatBase(world, seatName); err == nil {
+			bases[seatName] = base
+		}
+	}
+	return bases
 }
 
 // servedPort is a served port as text, however the manifest and the node's settings carried it.