session.close only closed the slash_worker subprocess but never called
agent.close() on the AIAgent instance. In the long-lived TUI gateway
process, this left httpx clients for GC to finalize. When the OS
recycled a closed FD number for a new active connection, the stale
finalizer would close the live socket, causing intermittent
[Errno 9] Bad file descriptor on subsequent LLM API calls.
Call agent.close() (which properly shuts down the httpx transport pool
and TCP sockets) before closing the slash_worker.
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