feat: add last message preview to session picker

Read the final user/assistant message from session transcripts and display
it in the picker alongside the session update time. Allows quick previews
of what's in each session without opening it.

src/tui/gateway-chat.ts

@@ -65,6 +65,7 @@ export type GatewaySessionList = {
     lastTo?: string;
     lastAccountId?: string;
     derivedTitle?: string;
+    lastMessagePreview?: string;
   }>;
 };
 
@@ -185,6 +186,7 @@ export class GatewayChatClient {
       includeGlobal: opts?.includeGlobal,
       includeUnknown: opts?.includeUnknown,
       includeDerivedTitles: opts?.includeDerivedTitles,
+      includeLastMessage: opts?.includeLastMessage,
       agentId: opts?.agentId,
     });
   }

src/tui/tui-command-handlers.ts

@@ -155,21 +155,30 @@ export function createCommandHandlers(context: CommandHandlerContext) {
         includeGlobal: false,
         includeUnknown: false,
         includeDerivedTitles: true,
+        includeLastMessage: true,
         agentId: state.currentAgentId,
       });
       const items = result.sessions.map((session) => {
         const title = session.derivedTitle ?? session.displayName;
         const formattedKey = formatSessionKey(session.key);
+        // Avoid redundant "title (key)" when title matches key
+        const label =
+          title && title !== formattedKey ? `${title} (${formattedKey})` : formattedKey;
+        // Build description: time + message preview
+        const timePart = session.updatedAt ? formatRelativeTime(session.updatedAt) : "";
+        const preview = session.lastMessagePreview?.replace(/\s+/g, " ").trim();
+        const description = preview ? `${timePart} · ${preview}` : timePart;
         return {
           value: session.key,
-          label: title ? `${title} (${formattedKey})` : formattedKey,
-          description: session.updatedAt ? formatRelativeTime(session.updatedAt) : "",
+          label,
+          description,
           searchText: [
             session.displayName,
             session.label,
             session.subject,
             session.sessionId,
             session.key,
+            session.lastMessagePreview,
           ]
             .filter(Boolean)
             .join(" "),