Did the materials list or work description include buying corner pieces? Or mitered edges? What was specified in the front end design documents that you used to have contractors bid on? What was the corner treatment promised in the written contract from the contractor?

What was the labor cost for this? 8-10K? $800-$1000? $100 and a case of natty lite?

No, the work description didn't discuss buying corner pieces. That's my ignorance as I didn't even know they existed until now. The work description just summarized the size of the large accent wall they were installing. In addition they built a bar that they knew would obviously have corners. I spent 20K with them.

Spending 25K with a Design and Build firm, or a separate 5K up front on a designer, would have yielded the better result that you had in your head, that never made it to the printed paper. Nothing to be done at this stage, unless you’re willing to pay to redo it all.