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/notes.rs

@@ -264,24 +264,27 @@ impl McpTool for GenerateStandupReportHandler {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use tempfile::tempdir;
     use serde_json::json;
+    use tempfile::tempdir;
 
     #[tokio::test]
     async fn test_notes_lifecycle() {
         let dir = tempdir().unwrap();
         let state = Arc::new(MemoryState::new(dir.path().to_str().unwrap()));
-        
+
         let add_handler = AddStickyNoteHandler;
         let args = json!({
             "content": "Buy milk",
         });
-        
+
         let res = add_handler.execute(args, state.clone()).await.unwrap();
         assert!(res.contains("Sticky note added"));
 
         let read_handler = ReadStickyNotesHandler;
-        let res2 = read_handler.execute(json!({}), state.clone()).await.unwrap();
+        let res2 = read_handler
+            .execute(json!({}), state.clone())
+            .await
+            .unwrap();
         assert!(res2.contains("Buy milk"));
 
         let delete_handler = DeleteStickyNoteHandler;
@@ -289,7 +292,10 @@ mod tests {
         let res3 = delete_handler.execute(args2, state.clone()).await.unwrap();
         assert_eq!(res3, "Sticky note deleted.");
 
-        let res4 = read_handler.execute(json!({}), state.clone()).await.unwrap();
+        let res4 = read_handler
+            .execute(json!({}), state.clone())
+            .await
+            .unwrap();
         assert!(!res4.contains("Buy milk"));
     }
 
@@ -297,19 +303,22 @@ mod tests {
     async fn test_handoff_and_summaries() {
         let dir = tempdir().unwrap();
         let state = Arc::new(MemoryState::new(dir.path().to_str().unwrap()));
-        
+
         let handoff_handler = LeaveHandoffMemoHandler;
         let args = json!({
             "content": "Finished implementing graph tests",
             "author": "Antigravity",
             "namespace": "global"
         });
-        
+
         let res = handoff_handler.execute(args, state.clone()).await.unwrap();
         assert_eq!(res, "Handoff memo left");
 
         let read_handoff = ReadHandoffMemosHandler;
-        let res2 = read_handoff.execute(json!({"namespace": "global"}), state.clone()).await.unwrap();
+        let res2 = read_handoff
+            .execute(json!({"namespace": "global"}), state.clone())
+            .await
+            .unwrap();
         assert!(res2.contains("Finished implementing graph tests"));
 
         let summary_handler = AddSessionSummaryHandler;
@@ -317,11 +326,20 @@ mod tests {
             "summary": "Completed a bunch of tests",
             "namespace": "global"
         });
-        let res3 = summary_handler.execute(args_sum, state.clone()).await.unwrap();
+        let res3 = summary_handler
+            .execute(args_sum, state.clone())
+            .await
+            .unwrap();
         assert_eq!(res3, "Session summary added");
-        
+
         let standup_handler = GenerateStandupReportHandler;
-        let res4 = standup_handler.execute(json!({"namespace": "global", "hours_lookback": 24}), state.clone()).await.unwrap();
-        assert!(res4.len() > 0);
+        let res4 = standup_handler
+            .execute(
+                json!({"namespace": "global", "hours_lookback": 24}),
+                state.clone(),
+            )
+            .await
+            .unwrap();
+        assert!(!res4.is_empty());
     }
 }