I worked at Yahoo some years later and the process was the same when I was there.

Yes, people generally put two and two together when there was a calendar invite with their manager and HR.

We were in a European office though, so layoffs aren't American-style "escorted from the office with immediate effect".

Not explicitly, but there were rumors a few days before. Also the signs were there: every single meeting room was booked, meeting rooms all had water & tissues, etc.