…cherry-pick #18647) (#18649)

Co-authored-by: dependabot[bot]
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

…ick #18673) (#18676)

Cherry-picked fix: stop tearing down non-TTY processes on SSH session
end (#18673)

(possibly temporary) fix for #18519

Matches OpenSSH for non-tty sessions, where we don't actively terminate
the process.

Adds explicit tracking to the SSH server for these processes so that if
we are shutting down we terminate them: this ensures that we can shut
down quickly to allow shutdown scripts to run. It also ensures our tests
don't leak system resources.

Co-authored-by: Spike Curtis <spike@coder.com>

…ry-pick #18680) (#18697)

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Garrett Delfosse <garrett@coder.com>

Co-authored-by: Danny Kopping <danny@coder.com>
Co-authored-by: Steven Masley <Emyrk@users.noreply.github.com>
Co-authored-by: Bruno Quaresma <bruno@coder.com>
Co-authored-by: Sas Swart <sas.swart.cdk@gmail.com>
Co-authored-by: Susana Ferreira <susana@coder.com>
Co-authored-by: Danielle Maywood <danielle@themaywoods.com>
Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Asher <ash@coder.com>
Co-authored-by: Hugo Dutka <hugo@coder.com>