Some bundled CPython runtime builds strip stdlib ThreadPoolExecutor's
copy_context() propagation, so work submitted to the daemon pool runs in a
bare context. Under the multiplexed gateway this dropped the profile
secret scope in pool workers: the context-compression timeout fence
resolved auxiliary provider keys (SURPLUS_API_KEY) with
UnscopedSecretError, silently degrading LLM compression to lossy
deterministic summaries and driving re-read loops in affected sessions.
Restore stdlib semantics in submit() by snapshotting the caller's context
and running the callable inside it (a no-op re-application on runtimes
that already propagate). Mirrors the gateway's
_run_in_executor_with_context pattern.
Tests: daemon pool worker sees caller contextvars; scoped get_secret works
in a daemon-pool worker under multiplex while scoped misses still fail
closed (no env leak).
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