Containers used `sleep infinity` as PID 1, which never reacts to
SIGTERM: the kernel does not apply default signal dispositions to PID 1,
and sleep has no SIGTERM handler, so every `podman stop` silently
ignored the signal, waited out the full 10-second grace period, and fell
back to SIGKILL.
PID 1 now traps TERM and INT itself and exits on request, so one-off
manual stops of a still-running agent container end immediately instead
of after the kill timeout.
The PID 1 command is baked in at create time, so containers predating
this change are detected and recreated automatically on the next run.
The upgrade swaps the runtime under the user's feet, and nothing reuses
the old Docker containers or image: storage moves to
~/.local/share/containers, the image has to be rebuilt, and hosts
without subuid/subgid mappings fail on the first run. Without notes that
say so, the empty container list looks like data loss and the first
failed start looks like a broken release.
