ASSERT_DEBUG
ASSERT_DEBUG(nbytes > rem, "invariant");
ASSERT_DEBUG(nbytes != 0, "invariant");
ASSERT_DEBUG(keysz == FX_CHACHA20_KEYSIZE, "keysz: %zu", keysz);
ASSERT_DEBUG(rng->brng_generation > 0, "root RNG not seeded");
ASSERT_DEBUG(atomic_load_acq_64(&fxrng_root_generation) != 0,
ASSERT_DEBUG(event->he_size <= sizeof(event->he_entropy),
ASSERT_DEBUG(n > 0 && n <= FXRNG_NPOOLS, "n:%u", n);
ASSERT_DEBUG(len == FX_CHACHA20_KEYSIZE, "chacha20 uses 256 bit keys");