Some of the cloud hosting NTP environments abolish leaps by smearing them out over a long period. That's one way to help out application code unprepared for them.

More surprising is that a number of expensive, precision, commercial GPS chips do NOT all handle leap seconds the same way. I worked in a shop that used about three different ones for their PPS and clock outputs and we got about three different behaviors from them. Evidently the leap seconds are broadcast in supplementary data and then applied on chip when it produces a UTC output.

No server environment will ever see it. Any sane person will immediately understand this is going to break too much stuff and it is not worth educating thousands of developers.

Everybody just smears it over some period of time.