Static RELEASE_TIMER_BACKEND 

static RELEASE_TIMER_BACKEND: AtomicU8

The process-wide release thread’s backend, or BACKEND_NONE.

Monotonic: written exactly once, by the construction of the process-wide wheel, and never cleared. That monotonicity is what makes release_timer_started sound to assert on from a test that shares a binary with other tests — in the true direction. The tests that assert false are isolated into a test binary of their own, because false → true is the direction that can be spoiled.