refactor: Implement unified search abstraction, MemoryState refactoring, error handling, and unit test expansion

server/src/api/rest.rs

@@ -121,10 +121,12 @@ mod tests {
     async fn test_gate_handlers() {
         let dir = tempdir().unwrap();
         let state = Arc::new(MemoryState::new(dir.path().to_str().unwrap()));
+        let (shutdown_tx, _) = tokio::sync::oneshot::channel();
         let app_state = Arc::new(AppState {
             handler: Arc::new(MemoryHandler::new(state.clone())),
             clients: RwLock::new(HashMap::new()),
             next_id: AtomicUsize::new(1),
+            shutdown_tx: std::sync::Mutex::new(Some(shutdown_tx)),
         });
 
         // Set a gate to authorized