fix: doc set_topic_name + clear archivedAt

docs/tools/slash-commands.md

@@ -99,6 +99,7 @@ Text + native (when enabled):
 - `/dock-telegram` (alias: `/dock_telegram`) (switch replies to Telegram)
 - `/dock-discord` (alias: `/dock_discord`) (switch replies to Discord)
 - `/dock-slack` (alias: `/dock_slack`) (switch replies to Slack)
+- `/set_topic_name <name>` (Telegram topics only)
 - `/activation mention|always` (groups only)
 - `/send on|off|inherit` (owner-only)
 - `/reset` or `/new [model]` (optional model hint; remainder is passed through)

src/auto-reply/reply/session.ts

@@ -442,7 +442,7 @@ export async function initSessionState(params: {
     archivedAt: baseEntry?.archivedAt,
   };
   if (typeof sessionEntry.archivedAt === "number") {
-    sessionEntry.archivedAt = null;
+    sessionEntry.archivedAt = undefined;
   }
   const metaPatch = deriveSessionMetaPatch({
     ctx: sessionCtxForState,