Validate workflow rule writes

MeetingAssistant/Workflow/WorkflowRulesEditorTools.cs

@@ -120,7 +120,7 @@ public sealed class WorkflowRulesEditorTools
         var updated = replace_file
             ? yaml
             : AgentFileToolContent.AppendContent(existing, yaml);
-        var validation = ValidateYaml(updated);
+        var validation = await ValidateYamlAsync(updated);
         if (validation is not null)
         {
             return validation;
@@ -930,22 +930,27 @@ public sealed class WorkflowRulesEditorTools
         }
     }
 
-    private static string? ValidateYaml(string yaml)
+    private static async Task<string?> ValidateYamlAsync(string yaml)
     {
         if (string.IsNullOrWhiteSpace(yaml))
         {
             return null;
         }
 
+        MeetingWorkflowRulesFile rulesFile;
         try
         {
-            _ = YamlDeserializer.Deserialize<MeetingWorkflowRulesFile>(yaml);
-            return null;
+            rulesFile = YamlDeserializer.Deserialize<MeetingWorkflowRulesFile>(yaml) ?? new MeetingWorkflowRulesFile();
         }
         catch (YamlException exception)
         {
             return $"Refused: workflow rules YAML is invalid. {exception.Message}";
         }
+
+        var errors = await MeetingWorkflowRulesValidator.ValidateAsync(rulesFile);
+        return errors.Count == 0
+            ? null
+            : "Refused: workflow rules are invalid. " + string.Join(" ", errors);
     }
 
     private async Task WriteRecommendedProjectSeedAsync(string projectRoot, string projectName)