kern/60757: entering and leaving ddb leaves wscons confused

["uwe%stderr.spb.ru@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60757
>Category:       kern
>Synopsis:       entering and leaving ddb leaves wscons confused
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Sep 20 18:10:00 +0000 2026
>Originator:     Valery Ushakov
>Release:        NetBSD 11.0
>Organization:
>Environment:
NetBSD omena 11.0 NetBSD 11.0 (GENERIC) #0: Thu Jul 30 15:23:12 UTC 2026  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64

>Description:
After entering DDB from wscons from a secondary screen (ttyE1+)
and leaving it, the wscons is confused about which screen it is on.

>How-To-Repeat:
Switch to a secondary wscons screen (say, ttyE1) then hit
<Ctrl>-<Alt>-<Esc> to enter DDB.  Note that wscons switches to ttyE0
(constty) before entering DDB.  Now leave DDB with `c` (continue).

Wscons is now in a weird state.  Press enter a few times, as you would
- nothing seems to happen.  The machine appears wedged at first sight,
except an ssh session from another machine seems to run fine.  %-|

What actually happens is that wscons is left in a weird superposition.
Those enters are sent to the terminal you were at when you hit
C-A-Esc, it's just you are not shown that terminal, so you don't see
any output that happens over there - you are shown ttyE0.  Except that
when you try to switch back to ttyE1 - you can't, b/c wscons thinks
you are already there and nothing needs to be done.  You need to
switch to any other terminal first - ttyE2, etc, or even to ttyE0
(though you won't get any visual confirmation of that, obviously, as
you are already shown ttyE0).  _Now_ you can switch back to ttyE1
where you started.

>Fix:
If we switch to ttyE0 before entering DDB, we should tell wscons about
it, probably.