Ooof, that's a doozy. Can definitely confirm that your concerns are valid. Do you know which linear drain was put in (ie, brand)?

I'll not tread into legal territory, but here are the obvious things I notice from your photos:

Plumbing code requires that your drain strainer remains removable/accessible for cleanout. That should have been tagged at your inspection. Pan should obviously be pitched correctly; it's difficult to tell from your photos, but if they left it pitched only in one plane and closed up the sides of the drain, that might cause the problem you're seeing. Re: the inside of the curb, I want to see a waterproofing membrane as the last layer before tile. It *could* be they used an old school PVC liner, but all of the linear drains with which I'm familiar are specified to be used with a topical membrane.

What did the build process look like? How was the slope retrofit for the curbless achieved? How was the waterproofing done?

The pitch to the drain looks all wrong and I'm not sure what I'm looking at in the second photo, but it looks like a disaster. What type of tile did you use on the floor? I get the feeling this might be a gut job...mostly based on the second photo.

What exactly is the hot mess in photo #2? Is that the inside of a curb? What is the brown muck?

Back up, take some more photos for context. Any more photos or description of the process BEFORE tile was installed? And yes, what exactly is going on with photo #2?

Were they going for some "infinity edge" shower drain? I mean where IS your drain? it is allegedly "hidden" under the tiles and the water goes down the slit?

Oh my.

Imagine expecting a tile installer to know that water flows downhill.

Since a curbless shower and linear drain were mentioned, if anyone is interested, the current season of This Old House has an episode in which they installed the drain and shower pan for a curbless shower and linear drain. It is Season 43, episode 13. Here is a link to the episode. The drain installation starts at minute 17:38, and is about 5 minutes long. I expect that the tile installation will be shown in a future episode.

You can fast forward to 17:38 for the linear drain installation:

https://www.thisoldhouse.com/the-concord-country-cape/22866659/s43-e13-race-to-the-finish

Based on the photos, this seems to be well beyond being slightly off-kilter.

Call your contractor. Just tell him it appears there are myriad problems with the shower and to please call you back. If you get no reply...

Compose a letter. Just the facts, what problems do you see with the shower. Give him five business days from receipt for him to be on site and to come up with a plan for remediation. Since from your post you are leaning legal, which is your prerogative, the certified letter will get the 'legal ball' rolling. It's a formal notification requiring a formal reply.

Going legal can work. But it can drag things out. And even if you win, be it through legal representation or just appearing yourself in small claims court, collecting can be an issue. If you prefer legal, check into small claims court and what remediation you can expect from that. But also, how you can actually collect if it gets ruled in your favor.

It's best to give your contractor a chance to make things right. The thing is, with showers? Shower floor repairs often require a demo to the subfloor and restart. Band-aid or superficial fixes don't always work long-term where water is concerned. You bring in someone new to repair and their going to want to start from scratch. Because once they start work, they are now assuming responsibility for the end result. A competent tile mechanic is going to want to control his end result, and often times that means starting over from scratch.

Do understand if your GC hired the plumber to install the pan and the tiler to install the tile, this is between you and the GC. Not you and the plumber. Or you and the tiler. It's up to you to deal with the GC and the GC to deal with the people he hired.

And careful if your GC decides to give you the 'White Glove Treatment' by promising to fix it himself. Really? What credentials does he have? You want a pro to repair this, not an amateur in one field who is acting like an amateur in yet another field.

Good luck with whichever path you pursue.

@Shannon_WI I posted about this a week or so ago as I was surprised to see a copper pan still being used on TOH even if it's a MA renovation. They don't really show the critical parts of the drain installation ie the sloping of the mud bed and then the waterproofing of the drain and the mud bed. There are lots of example of how to do this on Youtube using the usual topical or sheet membrane products.

@Jeff Meeks - I just saw that episode yesterday on PBS so it was fresh in my mind. They mentioned the sloping of the mud bed, so perhaps they’ll show that in the next episode or two. Good to know there are lots of examples on Youtube, though it can be hard to know if the youtube video is a good one showing good instruction. I’ve heard there’s some bad ones on there by people just looking for likes but with not a lot of expertise.

@Shannon_WI @Jeff Meeks, "Good to know there are lots of examples on Youtube, though it can be hard to know if the youtube video is a good one showing good instruction. I’ve heard there’s some bad ones on there by people just looking for likes but with not a lot of expertise". Thanks for pointing that out. It is a real problem. Circles in the professional industry share some real doozies that are definitely not a service to the consumer or the industry. And HGTV is often the bane of our existence. Not ALL, but a lot are very, very bad indeed. There are a few reputable youtube tile channels owned by actual qualified professionals. Here's one example you can trust: https://www.youtube.com/c/saldiblasi

Sal is a terrific guy.

+1 on Sal.

Looking like we may have another runner.........................

Our Schluter linear drain top is removable and the filter underneath MUST be cleaned every few months.

+2 Sal is A Legend