perf: remove redundant MemoryState::deduplicate and resolve lock contention during index rebuild

server/src/handlers/graph.rs

@@ -534,7 +534,8 @@ impl McpTool for MergeEntitiesHandler {
             if let Some(src) = master.entities.remove(&req.source_entity) {
                 if let Some(tgt) = master.entities.get_mut(&req.target_entity) {
                     tgt.observations.extend(src.observations);
-                    MemoryState::deduplicate(&mut tgt.observations);
+                    tgt.observations.sort();
+                    tgt.observations.dedup();
                 } else {
                     let mut new_tgt = src.clone();
                     new_tgt.name = req.target_entity.clone();