_send waited for any output ending in "#", "$" or ">". netmiko matches that
against everything read so far, so a chunk that happened to end in such a
line ended the read while the command still ran. apt's bad-signature line,
"... <ftpmaster@ubuntu.com>", did exactly that: refresh_available_updates
returned half its output, and the rest -- exit status and prompt included --
arrived as the next command's output, so the update read after it failed
with "no exit status" (netOrk #615, seen on nine hosts on 2026-10-06).
A command that ends in "echo __NAME=$?" (__NETORK_RC=, and device-types'
__APT_RC= and __SVC_RC=) is now read until that marker, with a number, and
the prompt line after it. The echoed command line carries a literal $? and
cannot match. Every other command keeps the prompt pattern.
Christian Manivong