fix(mcp): propagate internal serialization errors instead of silently swallowing them to prevent LLM hallucination

server/src/handlers/tasks.rs

@@ -444,7 +444,10 @@ impl McpTool for UpdateMilestoneHandler {
         if found {
             Ok("Milestone updated".to_string())
         } else {
-            Err("Milestone not found. Please verify the milestone ID using list_milestones.".to_string())
+            Err(
+                "Milestone not found. Please verify the milestone ID using list_milestones."
+                    .to_string(),
+            )
         }
     }
 }