Name the error of a fetch whose lock waits for an unpublished package (issue 1587, ADR 0500 §6)

waits for: is the prefix the builder turns into a queued key with Waits; it is not
one of the errors held until the fingerprint changes.

go/delivery/builder.go

@@ -147,6 +147,9 @@ const (
 	VersionTaken = "version taken: "
 	// RefusedKind: no build module builds this kind of artifact in its language.
 	RefusedKind = "refused kind: "
+	// WaitsFor: a fetch found the module's lock naming a package version the registry does not hold yet; the builder
+	// writes the key queued with Waits (novox/hq ADR 0500 clause 6), and it is built once the package is published.
+	WaitsFor = "waits for: "
 )
 
 // FailedUntilChanged says whether a failed key's error is one that is not built again until the module's fingerprint

go/delivery/builder_reference_test.go

@@ -133,3 +133,11 @@ func TestADoneKeyWithNoArtifactIsReferenced(t *testing.T) {
 		t.Fatalf("Referenced = %v, %v; want true", ok, missing)
 	}
 }
+
+// A Node fetch that finds the lock naming a package version the registry does not hold fails with WaitsFor; the
+// builder then writes the key queued with Waits, and the error is not one that waits for the fingerprint to change.
+func TestWaitsForIsAPrefixThatIsBuiltAgain(t *testing.T) {
+	if WaitsFor != "waits for: " || FailedUntilChanged(WaitsFor+"@novox/mesh-sdk@0.1.15") {
+		t.Fatalf("WaitsFor = %q", WaitsFor)
+	}
+}