fix: revalidate externally changed LXC state

AppImage/lib/lxc-update-observation.ts

@@ -0,0 +1,21 @@
+import { fetchApi } from "./api-config"
+
+interface UpdateObservation {
+  last_check?: string | null
+  stale?: boolean
+  stale_after_seconds?: number
+}
+
+export function isLxcUpdateStale(observation?: UpdateObservation, now = Date.now()): boolean {
+  if (!observation || observation.stale === true) return true
+  const checked = Date.parse(observation.last_check || "")
+  const age = now - checked
+  const limit = (observation.stale_after_seconds ?? 86400) * 1000
+  return !Number.isFinite(checked) || age < 0 || age >= limit
+}
+
+// Called only by the OS section's explicit button. Uses installed package
+// state and existing indexes; fetching this never upgrades or refreshes APT.
+export function checkLxcUpdates<T>(vmid: number): Promise<T> {
+  return fetchApi<T>(`/api/vms/${vmid}/updates/check`, { method: "POST" })
+}