fix(campaign): name every missing required flag, in flag order

Five required flags ranged as a map, so omitting three told the operator
about one, chosen at random.

cmd/internal-tools/campaign/main.go

@@ -74,17 +74,26 @@ func parseArguments(arguments []string, stderr io.Writer) (config, error) {
 	}
 	configuration.extraArguments = flagSet.Args()
 
-	for name, value := range map[string]string{
-		"--spec":      configuration.specPath,
-		"--bundle-id": configuration.bundleID,
-		"--arm":       configuration.arm,
-		"--seeds":     seedSpecification,
-		"--output":    configuration.outputDirectory,
+	// Every missing flag is named together, in flag order: stopping at the
+	// first turns one rerun into one rerun per missing flag.
+	var missing []error
+	for _, required := range []struct {
+		name  string
+		value string
+	}{
+		{"--spec", configuration.specPath},
+		{"--bundle-id", configuration.bundleID},
+		{"--arm", configuration.arm},
+		{"--seeds", seedSpecification},
+		{"--output", configuration.outputDirectory},
 	} {
-		if value == "" {
-			return config{}, fmt.Errorf("%s is required", name)
+		if required.value == "" {
+			missing = append(missing, fmt.Errorf("%s is required", required.name))
 		}
 	}
+	if err := errors.Join(missing...); err != nil {
+		return config{}, err
+	}
 	switch configuration.platform {
 	case "android", "ios", "web":
 	default:

cmd/internal-tools/campaign/main_test.go

@@ -71,6 +71,35 @@ func TestParseArguments_Rejections(t *testing.T) {
 	}
 }
 
+// Three flags missing is one rerun, not three: the operator is told about all
+// of them at once, in flag order, whatever order the check happened to walk.
+func TestParseArguments_NamesEveryMissingRequiredFlagInFlagOrder(t *testing.T) {
+	_, err := parseArguments(
+		[]string{"--bundle-id", "a", "--seeds", "1", "--max-steps", "10"},
+		io.Discard,
+	)
+	if err == nil {
+		t.Fatal("got no error, want every missing flag named")
+	}
+	message := err.Error()
+	previous := -1
+	for _, name := range []string{"--spec", "--arm", "--output"} {
+		at := strings.Index(message, name)
+		if at < 0 {
+			t.Fatalf("got %q, want %s named", message, name)
+		}
+		if at < previous {
+			t.Errorf("got %q, want the flags named in flag order", message)
+		}
+		previous = at
+	}
+	for _, supplied := range []string{"--bundle-id", "--seeds"} {
+		if strings.Contains(message, supplied) {
+			t.Errorf("got %q, want the supplied %s left out", message, supplied)
+		}
+	}
+}
+
 func TestRunArguments_PlatformDeviceFlagAndPassthrough(t *testing.T) {
 	cases := []struct {
 		platform string