perf(tasks): refactor update and delete task handlers to eliminate string clones when mapping task relationships by relying on reference closures and index queues

server/src/handlers_v2/tasks.rs

@@ -206,16 +206,26 @@ impl McpTool for UpdateTaskStatusHandler {
 
                 // Cascade cancellation to children
                 if target_status == "cancelled" || target_status == "abandoned" {
-                    let mut children_map: std::collections::HashMap<String, Vec<usize>> =
+                    let mut children_map: std::collections::HashMap<usize, Vec<usize>> =
                         std::collections::HashMap::new();
+                    
+                    // First pass: map string ID to index to build the adjacency list by index
+                    let mut id_to_idx = std::collections::HashMap::new();
+                    for (idx, t) in tasks.iter().enumerate() {
+                        id_to_idx.insert(t.id.as_str(), idx);
+                    }
+
                     for (idx, t) in tasks.iter().enumerate() {
                         if let Some(pid) = &t.parent_id {
-                            children_map.entry(pid.clone()).or_default().push(idx);
+                            if let Some(&p_idx) = id_to_idx.get(pid.as_str()) {
+                                children_map.entry(p_idx).or_default().push(idx);
+                            }
                         }
                     }
 
+                    if let Some(&start_idx) = id_to_idx.get(target_id.as_str()) {
                         let mut queue = std::collections::VecDeque::new();
-                    queue.push_back(target_id.clone());
+                        queue.push_back(start_idx);
 
                         while let Some(curr) = queue.pop_front() {
                             if let Some(child_indices) = children_map.get(&curr) {
@@ -224,7 +234,8 @@ impl McpTool for UpdateTaskStatusHandler {
                                         && tasks[idx].status != target_status
                                     {
                                         tasks[idx].status = target_status.clone();
-                                    queue.push_back(tasks[idx].id.clone());
+                                        queue.push_back(idx);
+                                    }
                                 }
                             }
                         }