My understanding is that shortened variable names are recommended for small, tight contexts (loops, short functions) but not generally.

That and conventionally standard names, like r for request/reader, w for writer, etc.

Agreed. Functions shouldn’t be full of short non-descriptly named variables.

The longer the lifetime/scope of a variable, and the more variables there are, the more descriptive the names should be.

These are dang short compared to Java's FooBarBazBeanFactoryFuncClassImpl. The point you may be responding to is that "Short variable names" are themselves contextual. If you're doing a simple loop:

  for i := range personlist {
    person := personlist[i]
    ...
  }

Is more readable than

  for personNum := range personlist {
    person := personlist[personNum]
    ...
  }

because it makes clear that the i is basically irrelevant. The latter isn't bad style if you're three loops deep, because i, j, k is a bit harder to keep track of which is which.