Identify configuration source files in load errors

internal/cli/configkit_load.go

@@ -30,6 +30,18 @@ func writeConfigLoadError(output io.Writer, err error) {
 	var loadError *configkit.LoadError
 	if errors.As(err, &loadError) {
 		if writeErr := configkit.WriteDiagnostics(output, loadError.Diagnostics()); writeErr == nil {
+			// ConfigKit's locations contain source IDs. Keep its renderer and
+			// supply the acquired-source legend so imported/profile errors can
+			// be traced to a file. Quoting also escapes terminal controls.
+			for _, source := range loadError.Sources() {
+				label := source.Path
+				if label == "" {
+					label = source.Label
+				}
+				if _, err := fmt.Fprintf(output, "source %q: %q\n", source.ID, label); err != nil {
+					return
+				}
+			}
 			return
 		}
 	}