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/settings.go

@@ -173,9 +173,14 @@ func UnusedSettings(m Manifest, layers []Layer) []string {
 		return nil
 	}
 
+	// A key a file's content asks for with ${setting:<key>} is a destination too (ADR 0155).
+	asked := settingKeysUsedBy(m)
 	var unused []string
 	for _, layer := range layers {
 		for key := range layer.Values {
+			if asked[key] {
+				continue
+			}
 			// `expose` is a real destination for a module that listens: it overrides a port's
 			// source (novox/hq ADR 0046), validated in Exposure, so it is not stray here.
 			if key == ExposeSetting && len(m.Listens) > 0 {