My impression was that the trough or "catch basin" as you called it, could be left exposed like this, or could be covered with a steel grate. At that point, it would look like a linear drain. Our linear drain is actually built sort of like this, in the sense that it just has a round drain in the middle of a trough, it's just covered up with a linear piece-- tiled, in our case, to become "invisible." I agree, I'd rather have it disappear. I don't think I ever stand that close to the wall, but it does look sort of disturbing. These guys build very high end and what look to be thought-out houses, so I would be very surprised if they didn't have the waterproofing figured out. But maybe not enough detail here to take away and DIY. I just know I looked at and for an awful lot of examples of curbless designs and didn't always find what I was looking for. (Maybe I'll post mine here if the grout ever gets sealed and the glass guy installs the side panel.)

If you want to get to the bottom of why the tips blackened in the first place and how to avoid that in the future, we'd have to know more about their winter conditions...temperature, humidity, light, duration of time 'dormant', watering, when you brought them in in the fall, etc. Typically when tips are damaged this way, they abort and it can take a lot longer for them to regenerate new growing tips. Sometimes even into July or August. So your growing season this year is severely shortened. Best to keep your plants from stressing to the point where they get black tip in the first place.

Thank you so much.

I'm afraid there are several other areas out there like this. There are a lot of peoplewho would love to help them, but are going to areas where there is currently too much help and are getting turned away. Sharing the story where it will get more publicity may help them to get more help directed their way.