I saw a bright flash on the moon opposite the remaining sunlit sliver at 04:41:43, right before the beginning of totality. I ran inside and checked the timeanddate webcast from Morocco and it was visible there too (see https://imgur.com/VSpNGVi), so it wasn't an airplane or something else local. It was also visible on the Griffith Observatory webcast (see https://imgur.com/HRVUAxL).
Could this have been a meteor impact on the moon? The fact that it was visible from Morocco and California as well as my location in the Northeast United States would seem to rule out something like a straight-on meteor in the Earth's atmosphere (although I did see a shooting star right near the moon a bit before I saw the flash).