When a fleet host has no container runtime at all (e.g. a native
postfix/dovecot mail server), `docker ps` returns "sh: docker: not
found". The page surfaced that raw shell text inside a red error box,
which reads as a broken feature — the user reasonably expected the tab
to show containers.
Probe `available()` first: if the docker binary is genuinely absent,
render a clean, neutral "Docker nicht installiert — es gibt keine
Container zum Anzeigen" panel (box icon, no alarm styling) rather than
the shell error. A real fault (daemon down / permission) still shows
the actual error as before. Verified end-to-end against a real SSH host
with no runtime (the honest state) and against a real docker host (full
container list + Logs/Restart/Stop actions render).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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