internal/pkg: populate substitute status

These are not created when taking the fast path, but should be inherited from the alternative.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/pkg_test.go

@@ -1059,8 +1059,14 @@ func TestCache(t *testing.T) {
 						"_EmV5nsYZ2UWHgRmLDMU8i-rJWDx-kv5_1pFrzQI7vMMCM5mAXivO8UZtVfOqMR_",
 					), want, nil},
 				})
-
 			}
+
+			if dents, err := os.ReadDir(base.Append("status").String()); err != nil {
+				t.Fatal(err)
+			} else if len(dents) > 0 {
+				t.Errorf("ReadDir: %v", dents)
+			}
+
 		}, expectsFS{
 			".": {Mode: fs.ModeDir | 0700},