The 5 service arms in appInstallCheckRequirements (traefik/gluetun/authelia/
headscale/prometheus) were identical _appReqServiceInstalled calls. Collapse them
into one generic default: any requirement naming a real container is a service
prerequisite — so a new service requirement now needs NO code here, just list it
in the app's CFG_<APP>_REQUIRES. domain + mail stay as their own special types; a
requirement that isn't a known app is still treated as a typo and ignored (safety
net preserved). Flavor messages kept via a small optional reason map
(_appReqServiceMsg); unknown-to-the-map services get a clean generic message.
Stays central (it's the requirements engine, not per-app logic) but is now
extensible without edits. Verified with stubs: met→rc0, absent service→flavor or
generic msg, brand-new container service→generic (zero code), typo→ignored.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Signed-off-by: librelad <librelad@digitalangels.vip>
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