The main thread polls nativeCallMessagesFromMainThread 146k times a second
with nothing to do. Between polls it now rests 100 us: nanosleep when the
governor is performance, TPAUSE (C0.2) when the CPU has WAITPKG, a spin
otherwise. Sleeping under a power-saving governor lets the render thread's
core clock down and drops frames, which is why TPAUSE is the default there.
MOCKTAIL_ENGINE_PUMP_REST=sleep|tpause|spin overrides. The profile trace
gains a slice for pumps that ran a message.
