Layer-2 defense for the FD-recycling race: even with
``force_close_tcp_sockets`` reduced to shutdown-only, the followup
``client.close()`` in ``_close_openai_client`` still walks the httpx
pool and closes sockets — and if called from a stranger thread (the
interrupt-check loop, the stale-call detector) it has the same
FD-recycling exposure that wrote a TLS record on top of ``kanban.db``.
Stamp the request_client_holder with the owning thread's ident at
``_set_request_client`` time. In ``_close_request_client_once``:
* Owning thread (the worker's ``finally``) → pop + ``client.close()``
via ``_close_request_openai_client``, exactly as before.
* Stranger thread → ``_abort_request_openai_client`` (new): only
``shutdown(SHUT_RDWR)`` the pool sockets and log a deferred-close
marker. The holder stays populated so the worker's eventual
``finally`` performs the real close from its own thread context,
where the FD release races nothing.
Applied symmetrically to both the non-streaming
``interruptible_api_call`` and the streaming variant — both routinely
get hit by stranger-thread interrupts.
The log field ``tcp_force_closed=N`` keeps its existing shape; the new
abort path adds ``deferred_close=stranger_thread`` so production
triage can distinguish the two close kinds.
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