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/builder/context_test.go

@@ -0,0 +1,26 @@
+package builder
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+)
+
+// A context on a seat is cloned from the base the mesh sent, joined to the repository's path; a
+// context by URL is itself; a seat the mesh sent no base for is refused by name (novox/hq ADR 0155).
+func TestAContextOnASeatIsClonedFromTheBaseTheMeshSent(t *testing.T) {
+	seats := map[string]string{"git": "http://forge.example.tld:3000"}
+	got, err := contextURL(catalogue.ArtifactContext{Seat: "git", Repository: "org/controller"}, seats)
+	if err != nil || got != "http://forge.example.tld:3000/org/controller.git" {
+		t.Fatalf("got %q, %v", got, err)
+	}
+	got, err = contextURL(catalogue.ArtifactContext{Repository: "https://elsewhere.example/x.git"}, seats)
+	if err != nil || got != "https://elsewhere.example/x.git" {
+		t.Fatalf("a URL context was changed: %q, %v", got, err)
+	}
+	_, err = contextURL(catalogue.ArtifactContext{Seat: "git", Repository: "org/controller"}, nil)
+	if err == nil || !strings.Contains(err.Error(), "git seat") {
+		t.Fatalf("a seat with no base was not refused by name: %v", err)
+	}
+}