Are your sure it is not either the back or sides?

I just glanced at the installation manual for the 36" 800 series Bosch and it has no such requirement. At least I didn't see it.

I don't see any such requirement in the Bosch 500 series or 800 series cooktop installation instructions. What model of Bosch cooktop are you referring to?

I would avoid the KA cooktop, for a variety of reasons.

I have a KA. Don't buy one if repetitive noises bother you. It is noisy. Love it otherwise.

I saw that in the manual, too, and I copied it and gave it to my custom cab guy so he could put an indentation in the top of the cab, as shown. But then my granite guy said he couldn't install the granite that way - surface has to be level - so he filled in the gap with epoxy and installed the granite. The cab guy said that because of the little rubber bumper spacers on the drawers, they don't close flush anyway, so there is a little open space at the top of the drawer. I decided that was close enough.

In practice, the drawer right under the KA cooktop does get warm inside if I cook something for a very long time. Just warm, though, certainly not warm enough to melt anything. Sometimes I open it an inch or two if it's getting warm.

I'd forgotten about that 3/16" slit thing. Yet another reason to avoid KA induction.

Just read the KA installation guide. I see what you are talking about. This is the first I've seen requiring a slit in the front. Gagg asks for one in the back. I think the solution to the countertop problem is to make the slits something like 5" long with a 1" separation between the slits. This gives support to the countertop.

If a custom-made cabinet, have the maker stain/seal the wood. If not custom, use some dark paint (black/brown/grey) to seal it.