fix(sasl): add delay between mechanism attempts

When EXTERNAL fails and PLAIN is tried immediately, the server may
not be ready. Add a 500ms delay before trying the next mechanism
to give the server time to reset the authentication state.

Changes:
- Add asyncio import at top of file
- Add _send_authenticate_after_delay() async method
- Create delayed task when trying next mechanism
- Remove inline asyncio import

plugins/core/sasl.py

@@ -25,6 +25,7 @@ Features:
 - Abort support via AUTHENTICATE *
 """
 
+import asyncio
 import base64
 import hashlib
 import hmac
@@ -1337,7 +1338,10 @@ class Sasl:
                     self._username, self._password, self._selected_mechanism
                 )
 
-            self.bot.send_line(f"AUTHENTICATE {self._selected_mechanism}")
+            # Small delay before trying next mechanism to let server reset
+            asyncio.get_event_loop().create_task(
+                self._send_authenticate_after_delay(self._selected_mechanism)
+            )
         else:
             self.bot.log.error("[SASL] No more mechanisms to try")
             self._authentication_in_progress = False
@@ -1347,6 +1351,11 @@ class Sasl:
             else:
                 self._finish_cap_negotiation()
 
+    async def _send_authenticate_after_delay(self, mechanism: str):
+        """Send AUTHENTICATE after a short delay."""
+        await asyncio.sleep(0.5)  # 500ms delay
+        self.bot.send_line(f"AUTHENTICATE {mechanism}")
+
     def _finish_cap_negotiation(self):
         """Complete CAP negotiation by sending CAP END."""
         if self._cap_negotiation_complete: