Harden PromptKit upgrade integration

internal/comparison/publish.go

@@ -519,8 +519,15 @@ func validateSafeErrorJSON(decoder *json.Decoder) error {
 }
 
 func validateRepairAttemptsJSON(decoder *json.Decoder) error {
+	var raw json.RawMessage
+	if err := decoder.Decode(&raw); err != nil {
+		return err
+	}
+	if bytes.Equal(bytes.TrimSpace(raw), []byte("null")) {
+		return fmt.Errorf("repairAttempts must be an integer")
+	}
 	var value int
-	if err := decoder.Decode(&value); err != nil {
+	if err := json.Unmarshal(raw, &value); err != nil {
 		return err
 	}
 	if value < 0 {