fix(mcp): convert silently swallowed OK string errors into explicit JSON-RPC errors for task transitions and bulk entity operations

server/src/handlers/graph.rs

@@ -221,15 +221,22 @@ impl McpTool for DeleteEntitiesHandler {
     async fn execute(&self, args: Value, state: Arc<MemoryState>) -> Result<String, String> {
         let req: DeleteEntitiesTool = serde_json::from_value(args).map_err(|e| e.to_string())?;
         let to_delete: std::collections::HashSet<_> = req.entity_names.into_iter().collect();
+        let mut missing = Vec::new();
         state.modify_graph(|master| {
             for name in &to_delete {
-                master.entities.remove(name);
+                if master.entities.remove(name).is_none() {
+                    missing.push(name.clone());
+                }
             }
             master
                 .relations
                 .retain(|r| !to_delete.contains(&r.from) && !to_delete.contains(&r.to));
         });
 
+        if !missing.is_empty() {
+            return Err(format!("Error: Entities not found: {}", missing.join(", ")));
+        }
+
         let idx = state
             .search_index
             .read()
@@ -292,10 +299,16 @@ impl McpTool for DeleteRelationsHandler {
 
     async fn execute(&self, args: Value, state: Arc<MemoryState>) -> Result<String, String> {
         let req: DeleteRelationsTool = serde_json::from_value(args).map_err(|e| e.to_string())?;
+        let mut missing_count = 0;
         state.modify_graph(|master| {
             let to_rem: HashSet<_> = req.relations.into_iter().collect();
+            let initial_len = master.relations.len();
             master.relations.retain(|r| !to_rem.contains(r));
+            missing_count = to_rem.len() - (initial_len - master.relations.len());
         });
+        if missing_count > 0 {
+            return Err(format!("Error: {} relation(s) not found in graph", missing_count));
+        }
         Ok("Relations deleted".to_string())
     }
 }

server/src/handlers/tasks.rs

@@ -257,7 +257,7 @@ impl McpTool for UpdateTaskStatusHandler {
         });
 
         if blocked {
-            Ok(format!(
+            Err(format!(
                 "Error: Cannot transition task. {}",
                 blocker_details
             ))