Force image editor to crop to original thumbnail size

I’ve searched high and low for this but think the answer I seek is being buried by the more common questions.

I am developing a theme for a client that has two specific image sizes (100×127 for thumbnail, 300×380 for medium). I have the media settings cropping like this when an image is uploaded, but if the user goes in to edit a thumbnail it doesn’t re-crop to the sizes specified in media settings.

What I am ideally looking for is either a plugin or something I can add to functions.php that will restrict the crop “draw” feature to the aspect ratio and then when the crop button is hit, will automatically resize the thumbnail to 100×127.

Does anything like this exist? I don’t even want the end user to have the option of entering in custom pixel sizes or aspect ratios. I’d rather that menu went away entirely.