Introduce internal/updates: a pure, I/O-free engine that decides what
should happen to each tracked platform component (Felis control-plane,
k3s, cloudflared, Velocity) given its current version, the latest
discovered upstream, its policy, and the current time.
Updates are never force-applied. A component is Pinned (Minecraft, left
alone), Notify (a SysAdmin is told and applies out of band), or Scheduled
(Felis may apply, but only inside a maintenance window the SysAdmin set).
The load-bearing invariants are unit-tested: a pinned component never
changes, a downgrade is never proposed, a prerelease is never
auto-applied, and an apply happens only inside the window.
Version parsing tolerates the real feeds (leading v, k3s +k3s1 build
suffix, calendar versions, prerelease tails) and orders by SemVer
precedence. ReleaseSource/Notifier/Applier are declared as integration
seams and exercised via fakes; this package ships no network, SMTP, or
kubectl, and deliberately has no blind k3s-upgrade applier.