A module-level asyncio.Lock binds to the loop it was first awaited on.
Under pytest-anyio (and xdist) each test spins up a new loop; any later
test that hit /health or /config would wait on a lock owned by a dead
loop and the whole worker would hang.
Create the lock on first use and drop it in the test-reset helpers so a
fresh loop always gets a fresh lock.
anti
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