In reply to https://jan.boddez.net/notes/8757c0b082. As such, I’m having …

As such, I’m having Imagick read the image data (works for all but ICO), and if that fails, use Imagick::setFormat('ico'). And it works! (Except for, well, emoji inside SVGs. A total edge case, I hope, but I’ve got a plan regardless.)