fix: prevent full message history from being sent to container agents

When lastAgentTimestamp was missing (new group, corrupted state, or
startup recovery), the empty-string fallback caused getMessagesSince to
return up to 200 messages — the entire group history. This sent a
massive prompt to the container agent instead of just recent messages.

Fix: recover the cursor from the last bot reply timestamp in the DB
(proof of what we already processed), and cap all prompt queries to a
configurable MAX_MESSAGES_PER_PROMPT (default 10). Covers all three
call sites: processGroupMessages, the piping path, and
recoverPendingMessages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/index.ts

@@ -9,6 +9,7 @@ import {
   getTriggerPattern,
   GROUPS_DIR,
   IDLE_TIMEOUT,
+  MAX_MESSAGES_PER_PROMPT,
   ONECLI_URL,
   POLL_INTERVAL,
   TIMEZONE,
@@ -33,6 +34,7 @@ import {
   getAllRegisteredGroups,
   getAllSessions,
   getAllTasks,
+  getLastBotMessageTimestamp,
   getMessagesSince,
   getNewMessages,
   getRouterState,
@@ -112,6 +114,27 @@ function loadState(): void {
   );
 }
 
+/**
+ * Return the message cursor for a group, recovering from the last bot reply
+ * if lastAgentTimestamp is missing (new group, corrupted state, restart).
+ */
+function getOrRecoverCursor(chatJid: string): string {
+  const existing = lastAgentTimestamp[chatJid];
+  if (existing) return existing;
+
+  const botTs = getLastBotMessageTimestamp(chatJid, ASSISTANT_NAME);
+  if (botTs) {
+    logger.info(
+      { chatJid, recoveredFrom: botTs },
+      'Recovered message cursor from last bot reply',
+    );
+    lastAgentTimestamp[chatJid] = botTs;
+    saveState();
+    return botTs;
+  }
+  return '';
+}
+
 function saveState(): void {
   setRouterState('last_timestamp', lastTimestamp);
   setRouterState('last_agent_timestamp', JSON.stringify(lastAgentTimestamp));
@@ -205,11 +228,11 @@ async function processGroupMessages(chatJid: string): Promise<boolean> {
 
   const isMainGroup = group.isMain === true;
 
-  const sinceTimestamp = lastAgentTimestamp[chatJid] || '';
   const missedMessages = getMessagesSince(
     chatJid,
-    sinceTimestamp,
+    getOrRecoverCursor(chatJid),
     ASSISTANT_NAME,
+    MAX_MESSAGES_PER_PROMPT,
   );
 
   if (missedMessages.length === 0) return true;
@@ -460,8 +483,9 @@ async function startMessageLoop(): Promise<void> {
           // context that accumulated between triggers is included.
           const allPending = getMessagesSince(
             chatJid,
-            lastAgentTimestamp[chatJid] || '',
+            getOrRecoverCursor(chatJid),
             ASSISTANT_NAME,
+            MAX_MESSAGES_PER_PROMPT,
           );
           const messagesToSend =
             allPending.length > 0 ? allPending : groupMessages;
@@ -500,8 +524,12 @@ async function startMessageLoop(): Promise<void> {
  */
 function recoverPendingMessages(): void {
   for (const [chatJid, group] of Object.entries(registeredGroups)) {
-    const sinceTimestamp = lastAgentTimestamp[chatJid] || '';
-    const pending = getMessagesSince(chatJid, sinceTimestamp, ASSISTANT_NAME);
+    const pending = getMessagesSince(
+      chatJid,
+      getOrRecoverCursor(chatJid),
+      ASSISTANT_NAME,
+      MAX_MESSAGES_PER_PROMPT,
+    );
     if (pending.length > 0) {
       logger.info(
         { group: group.name, pendingCount: pending.length },