Frame it in now. I just did a shower and did all the water proofing and then the bench. I used Kerdi membrane over backer board so the order of operations didn’t matter. You should be able to do the same thing here. Frame it, backer board over it, then water proof.

Here is a link to the final product. Final product

Edit again: Progress photos

I call it “mop head” cause that’s kinda how you make it

I’ve sold and installed shower doors for years. With tempered glass, any small hit on a corner or edge will do. My guys have had them explode while still wrapped from the factory and edge protected as they were carrying it.

I had a sliding door explode on me while trying to fix it. Not your FU, you just got caught holding the hot potato. Look in the corners of the other glass panel for a tempering logo. Then maybe talk to a local glass shop.

And, you have probably already learned this, please always wear shoes and safety glasses when dealing with glass.

So i would use a carbide grout removal tool. I found it works better with the plastic than the diamond grout saw.

https://www.lowes.com/pd/Marshalltown-Carbide-Bit-Red-Plastic-Grout-Remover/5001934083

Come on over to the Appalachian mountains. You can’t go wrong with Virginia, Tennessee, North Carolina, or Georgia! (Source: I lived many falls throughout the region.) It definitely beats the New England falls.