Problem

On gateway restart or adapter reconnect, connect() created a new commands.Bot instance without closing the previous one. Discord's gateway does not immediately terminate an orphaned websocket — both the old and new client remain live for a window of time. During that window, every inbound event is delivered to both connections independently.

MessageDeduplicator cannot prevent this because the two on_message coroutines may check is_duplicate before either has marked the ID as seen (race condition). The result: two separate agent turns are spawned per message, each producing a different response.

With auto_thread: true this is especially visible: one response lands in the thread (correct path) and a second response lands in the parent channel (incorrect path).

Fix

Before instantiating a new commands.Bot, await the old client's close() if it is not already closed, then clear _ready_event:

if self._client is not None and not self._client.is_closed():
    await self._client.close()
self._client = None
self._ready_event.clear()

This mirrors the guard already present in disconnect() (~line 779) and ensures only one Discord websocket is ever active for the adapter at any time.

Testing

• Gateway restart no longer produces double responses in any channel configuration
• auto_thread mode: only one response appears in the thread, no response leaks to the parent channel
• Single connect() call on first start: no change in behavior (self._client is None, guard is a no-op)

Closes #18187