Initially observed the problem after `nixpkgs` update sudo to 1.9.14p3 with a backport of https://github.com/sudo-project/sudo/commit/760c9c11074cb921ecc0da9fbb5f0a12afd46233.patch commit:

    https://github.com/NixOS/nixpkgs/pull/240681

This exposed a recent regression in sudo/main. Reproducer:

Good: newlines look as expected:

    # 1.9.14p3, no patches:
    $ { sudo printf "a\nb\nc\n" >&2; } |& nl
         1  a
         2  b
         3  c

Bad: newlines are like staircase (as if '\r' has no effect):

    # main, no patches:
    $ { sudo printf "a\nb\nc\n" >&2; } |& nl
         1  a
                  2 b
                          3 c

Bisect says it started since the following commit:

commit 760c9c11074cb921ecc0da9fbb5f0a12afd46233
Date:   Wed Jul 26 19:43:49 2023 -0600

    Don't assume that if std{in,out,err} is a tty, it is the user's tty.

    Previously, sudo only checked that the fd was a terminal, not that
    it matched sudo's idea of the user's terminal.  This matters when
    input or output is redirected to a different terminal.  In that
    case we want to interpose the fd with a pipe even if it refers to
    a terminal.  Bug #1056.