feat: add sessions preview rpc and menu prewarm

src/gateway/session-utils.types.ts

@@ -55,6 +55,22 @@ export type GatewayAgentRow = {
   };
 };
 
+export type SessionPreviewItem = {
+  role: "user" | "assistant" | "tool" | "system" | "other";
+  text: string;
+};
+
+export type SessionsPreviewEntry = {
+  key: string;
+  status: "ok" | "empty" | "missing" | "error";
+  items: SessionPreviewItem[];
+};
+
+export type SessionsPreviewResult = {
+  ts: number;
+  previews: SessionsPreviewEntry[];
+};
+
 export type SessionsListResult = {
   ts: number;
   path: string;