stop infinite retry loop when user blocks the bot or deactivates account

Forbidden from send_message was falling into the generic error handler,
which resets consecutive_errors to 0 right before the send attempt — so
backoff never grew past 60s and the pair retried forever, wasting request
queue capacity needed by other users' real periodic checks.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

LichessClientTG_bot/bot.py

@@ -13,6 +13,7 @@ from telegram.ext import (
     MessageHandler, filters, ContextTypes, ConversationHandler,
     PicklePersistence
 )
+from telegram.error import Forbidden
 
 import config
 from config import (
@@ -1822,11 +1823,25 @@ class LichessBot:
                     if not self.application:
                         raise RuntimeError(f"Application not initialized, cannot send notification for {gamer['username']} to user {user_id}")
 
-                    await self.application.bot.send_message(
-                        chat_id=user_id,
-                        text=notification,
-                        parse_mode='Markdown'
-                    )
+                    # Forbidden (user blocked the bot) is permanent, not worth retrying:
+                    # without this, consecutive_errors gets reset to 0 above right before
+                    # this call succeeds/fails, so the outer handler's backoff never grows
+                    # past 60s and this pair retries forever, wasting queue capacity that
+                    # other users' real checks need.
+                    try:
+                        await self.application.bot.send_message(
+                            chat_id=user_id,
+                            text=notification,
+                            parse_mode='Markdown'
+                        )
+                    except Forbidden:
+                        logger.warning(f"🚫 User {user_id} blocked the bot; stopping periodic monitoring for {gamer['username']}")
+                        self.db.set_user_gamer_period(user_id, gamer['id'], 0)
+                        if task_key in self.periodic_tasks:
+                            del self.periodic_tasks[task_key]
+                        if task_key in self.period_start_times:
+                            del self.period_start_times[task_key]
+                        return
                     logger.info(f"✅ Sent periodic notification for {gamer['username']} to user {user_id}")
                     # Increment periodic notification counter
                     self.counters.increment('periodic_notification')