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/gateway/protocol/schema/sessions.ts

@@ -9,6 +9,7 @@ export const SessionsListParamsSchema = Type.Object(
     includeGlobal: Type.Optional(Type.Boolean()),
     includeUnknown: Type.Optional(Type.Boolean()),
     includeDerivedTitles: Type.Optional(Type.Boolean()),
+    includeLastMessage: Type.Optional(Type.Boolean()),
     label: Type.Optional(SessionLabelString),
     spawnedBy: Type.Optional(NonEmptyString),
     agentId: Type.Optional(NonEmptyString),

src/gateway/session-utils.fs.ts

@@ -137,3 +137,53 @@ export function readFirstUserMessageFromTranscript(
   }
   return null;
 }
+
+const LAST_MSG_MAX_BYTES = 16384;
+const LAST_MSG_MAX_LINES = 20;
+
+export function readLastMessagePreviewFromTranscript(
+  sessionId: string,
+  storePath: string | undefined,
+  sessionFile?: string,
+  agentId?: string,
+): string | null {
+  const candidates = resolveSessionTranscriptCandidates(sessionId, storePath, sessionFile, agentId);
+  const filePath = candidates.find((p) => fs.existsSync(p));
+  if (!filePath) return null;
+
+  let fd: number | null = null;
+  try {
+    fd = fs.openSync(filePath, "r");
+    const stat = fs.fstatSync(fd);
+    const size = stat.size;
+    if (size === 0) return null;
+
+    const readStart = Math.max(0, size - LAST_MSG_MAX_BYTES);
+    const readLen = Math.min(size, LAST_MSG_MAX_BYTES);
+    const buf = Buffer.alloc(readLen);
+    fs.readSync(fd, buf, 0, readLen, readStart);
+
+    const chunk = buf.toString("utf-8");
+    const lines = chunk.split(/\r?\n/).filter((l) => l.trim());
+    const tailLines = lines.slice(-LAST_MSG_MAX_LINES);
+
+    for (let i = tailLines.length - 1; i >= 0; i--) {
+      const line = tailLines[i];
+      try {
+        const parsed = JSON.parse(line);
+        const msg = parsed?.message as TranscriptMessage | undefined;
+        if (msg?.role === "user" || msg?.role === "assistant") {
+          const text = extractTextFromContent(msg.content);
+          if (text) return text;
+        }
+      } catch {
+        // skip malformed
+      }
+    }
+  } catch {
+    // file error
+  } finally {
+    if (fd !== null) fs.closeSync(fd);
+  }
+  return null;
+}

src/gateway/session-utils.ts

@@ -22,7 +22,10 @@ import {
   parseAgentSessionKey,
 } from "../routing/session-key.js";
 import { normalizeSessionDeliveryFields } from "../utils/delivery-context.js";
-import { readFirstUserMessageFromTranscript } from "./session-utils.fs.js";
+import {
+  readFirstUserMessageFromTranscript,
+  readLastMessagePreviewFromTranscript,
+} from "./session-utils.fs.js";
 import type {
   GatewayAgentRow,
   GatewaySessionRow,
@@ -34,6 +37,7 @@ export {
   archiveFileOnDisk,
   capArrayByJsonBytes,
   readFirstUserMessageFromTranscript,
+  readLastMessagePreviewFromTranscript,
   readSessionMessages,
   resolveSessionTranscriptCandidates,
 } from "./session-utils.fs.js";
@@ -389,6 +393,7 @@ export function listSessionsFromStore(params: {
   const includeGlobal = opts.includeGlobal === true;
   const includeUnknown = opts.includeUnknown === true;
   const includeDerivedTitles = opts.includeDerivedTitles === true;
+  const includeLastMessage = opts.includeLastMessage === true;
   const spawnedBy = typeof opts.spawnedBy === "string" ? opts.spawnedBy : "";
   const label = typeof opts.label === "string" ? opts.label.trim() : "";
   const agentId = typeof opts.agentId === "string" ? normalizeAgentId(opts.agentId) : "";
@@ -503,15 +508,26 @@ export function listSessionsFromStore(params: {
   const finalSessions: GatewaySessionRow[] = sessions.map((s) => {
     const { entry, ...rest } = s;
     let derivedTitle: string | undefined;
-    if (includeDerivedTitles && entry?.sessionId) {
-      const firstUserMsg = readFirstUserMessageFromTranscript(
-        entry.sessionId,
-        storePath,
-        entry.sessionFile,
-      );
-      derivedTitle = deriveSessionTitle(entry, firstUserMsg);
+    let lastMessagePreview: string | undefined;
+    if (entry?.sessionId) {
+      if (includeDerivedTitles) {
+        const firstUserMsg = readFirstUserMessageFromTranscript(
+          entry.sessionId,
+          storePath,
+          entry.sessionFile,
+        );
+        derivedTitle = deriveSessionTitle(entry, firstUserMsg);
+      }
+      if (includeLastMessage) {
+        const lastMsg = readLastMessagePreviewFromTranscript(
+          entry.sessionId,
+          storePath,
+          entry.sessionFile,
+        );
+        if (lastMsg) lastMessagePreview = lastMsg;
+      }
     }
-    return { ...rest, derivedTitle } satisfies GatewaySessionRow;
+    return { ...rest, derivedTitle, lastMessagePreview } satisfies GatewaySessionRow;
   });
 
   return {

src/gateway/session-utils.types.ts

@@ -14,6 +14,7 @@ export type GatewaySessionRow = {
   label?: string;
   displayName?: string;
   derivedTitle?: string;
+  lastMessagePreview?: string;
   channel?: string;
   subject?: string;
   groupChannel?: string;

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(" "),