refactor: apply rust best practices and fix memory optimizations

- Optimized memory allocation in router.rs by offloading JSON serialization to spawn_blocking and using references.
- Prevented full graph duplication on startup in state.rs index rebuild.
- Eliminated massive String allocations in QueryGraphPathHandler BFS loops.
- Avoided temporary Strings in VisualizeGraphHandler via inline writing.
- Fixed O(N) full-graph deduplication in MergeEntitiesHandler to scale efficiently.

server/src/handlers/tasks.rs

@@ -491,26 +491,29 @@ impl McpTool for ListMilestonesHandler {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use tempfile::tempdir;
     use serde_json::json;
+    use tempfile::tempdir;
 
     #[tokio::test]
     async fn test_add_task_and_list() {
         let dir = tempdir().unwrap();
         let state = Arc::new(MemoryState::new(dir.path().to_str().unwrap()));
-        
+
         let add_handler = AddTaskHandler;
         let args = json!({
             "title": "Fix the hyperdrive",
             "description": "It's making a strange noise",
             "acceptance_criteria": ["Stop the noise", "Reach lightspeed"],
         });
-        
+
         let res = add_handler.execute(args, state.clone()).await.unwrap();
         assert!(res.contains("Task added with ID:"));
 
         let list_handler = ListActiveTasksHandler;
-        let res2 = list_handler.execute(json!({}), state.clone()).await.unwrap();
+        let res2 = list_handler
+            .execute(json!({}), state.clone())
+            .await
+            .unwrap();
         assert!(res2.contains("Fix the hyperdrive"));
     }
 
@@ -518,10 +521,16 @@ mod tests {
     async fn test_update_task_status() {
         let dir = tempdir().unwrap();
         let state = Arc::new(MemoryState::new(dir.path().to_str().unwrap()));
-        
+
         let add_handler = AddTaskHandler;
-        let res = add_handler.execute(json!({"title": "Test", "description": "test"}), state.clone()).await.unwrap();
-        
+        let res = add_handler
+            .execute(
+                json!({"title": "Test", "description": "test"}),
+                state.clone(),
+            )
+            .await
+            .unwrap();
+
         let id_start = res.find("ID: ").unwrap() + 4;
         let task_id = res[id_start..].trim();
 
@@ -532,9 +541,12 @@ mod tests {
         });
         let res3 = update_handler.execute(args, state.clone()).await.unwrap();
         assert_eq!(res3, "Task status updated.");
-        
+
         let list_handler = ListActiveTasksHandler;
-        let res4 = list_handler.execute(json!({}), state.clone()).await.unwrap();
+        let res4 = list_handler
+            .execute(json!({}), state.clone())
+            .await
+            .unwrap();
         assert!(!res4.contains(task_id));
     }
 
@@ -542,7 +554,7 @@ mod tests {
     async fn test_milestones_and_criteria() {
         let dir = tempdir().unwrap();
         let state = Arc::new(MemoryState::new(dir.path().to_str().unwrap()));
-        
+
         // Add Milestone
         let add_milestone = AddMilestoneHandler;
         let args_ms = json!({
@@ -555,7 +567,7 @@ mod tests {
         });
         let res1 = add_milestone.execute(args_ms, state.clone()).await.unwrap();
         assert!(res1.contains("Milestone added"));
-        
+
         // Fetch milestone ID from state directly to update
         let ms_id = state.milestones.read_with(|ms| ms[0].id.clone());
 
@@ -570,13 +582,22 @@ mod tests {
 
         // List Milestones
         let list_ms = ListMilestonesHandler;
-        let res3 = list_ms.execute(json!({"namespace": "global"}), state.clone()).await.unwrap();
+        let res3 = list_ms
+            .execute(json!({"namespace": "global"}), state.clone())
+            .await
+            .unwrap();
         assert!(res3.contains("completed"));
         assert!(res3.contains("Release 1.0"));
 
         // Task Acceptance Criteria
         let add_task = AddTaskHandler;
-        let res_task = add_task.execute(json!({"title": "Test", "description": "desc"}), state.clone()).await.unwrap();
+        let res_task = add_task
+            .execute(
+                json!({"title": "Test", "description": "desc"}),
+                state.clone(),
+            )
+            .await
+            .unwrap();
         let task_id = res_task[res_task.find("ID: ").unwrap() + 4..].trim();
 
         let set_ac = SetAcceptanceCriteriaHandler;
@@ -604,15 +625,31 @@ mod tests {
         let state = Arc::new(MemoryState::new(dir.path().to_str().unwrap()));
 
         let add_task = AddTaskHandler;
-        let parent = add_task.execute(json!({"title": "Parent", "description": "p"}), state.clone()).await.unwrap();
-        let parent_id = parent[parent.find("ID: ").unwrap() + 4..].trim().to_string();
+        let parent = add_task
+            .execute(
+                json!({"title": "Parent", "description": "p"}),
+                state.clone(),
+            )
+            .await
+            .unwrap();
+        let parent_id = parent[parent.find("ID: ").unwrap() + 4..]
+            .trim()
+            .to_string();
 
-        let child = add_task.execute(json!({"title": "Child", "description": "c", "parent_id": parent_id}), state.clone()).await.unwrap();
+        let child = add_task
+            .execute(
+                json!({"title": "Child", "description": "c", "parent_id": parent_id}),
+                state.clone(),
+            )
+            .await
+            .unwrap();
         let _child_id = child[child.find("ID: ").unwrap() + 4..].trim().to_string();
 
         let del_task = DeleteTaskHandler;
-        let res_del = del_task.execute(json!({"id": parent_id}), state.clone()).await.unwrap();
+        let res_del = del_task
+            .execute(json!({"id": parent_id}), state.clone())
+            .await
+            .unwrap();
         assert!(res_del.contains("Deleted task and its children (2 total)."));
     }
 }
-