Point standard output at standard error while a one-head delivery check runs, so its answer is the only JSON (issue 1311)

cmd/mesh-controller/delivery.go

@@ -902,16 +902,14 @@ func deliveryCommand(ctx context.Context, args []string) error {
 		if *group == "" && len(members) == 1 {
 			// One head, checked again as the forge's announcement would have it (a recheck): the controller's
 			// own path for a pull request, run because the delivery's owner asked.
-			// Its prose goes to standard error: standard output is the answer's JSON alone, or the seat verb
-			// reads no answer from it (novox/hq issue 1311).
-			var asked string
-			if err := sayingOnTheBus(ctx, inv, func() (err error) {
-				asked, err = (following{open: open, oneShot: true}).pullUpdated(ctx, members[0].pull(), os.Stderr)
-				return err
-			}); err != nil {
-				return err
-			}
-			return answer(recheckAnswer(asked, members[0].ID))
+			return recheckOneHead(members[0].ID, answer, func() (string, error) {
+				var asked string
+				err := sayingOnTheBus(ctx, inv, func() (err error) {
+					asked, err = (following{open: open, oneShot: true}).pullUpdated(ctx, members[0].pull(), os.Stderr)
+					return err
+				})
+				return asked, err
+			})
 		}
 		if *group == "" || len(members) < 2 {
 			return errors.New("delivery check --group <id> --members <json> (two heads or more), or --members <one head>")
@@ -1388,3 +1386,19 @@ func overNATS(conn *nats.Conn) (link.Bus, error) {
 func recheckAnswer(asked, member string) map[string]any {
 	return map[string]any{"asked": asked, "rechecked": member}
 }
+
+// recheckOneHead runs a one-head `delivery check` and answers it as data. Standard output is the answer's JSON alone,
+// or the seat verb reads no answer from it (novox/hq issue 1311): while the check runs, whatever it prints to standard
+// output (the controller's own path prints its prose there, as do the stores it reads) goes to standard error.
+func recheckOneHead(member string, answer func(any) error, ask func() (string, error)) error {
+	real := os.Stdout
+	os.Stdout = os.Stderr
+	asked, err := func() (string, error) {
+		defer func() { os.Stdout = real }()
+		return ask()
+	}()
+	if err != nil {
+		return err
+	}
+	return answer(recheckAnswer(asked, member))
+}