feat(catchup): scheduleOverdue helper for missed-window detection

internal/server/http/catchup.go

@@ -0,0 +1,29 @@
+// catchup.go — server-side catch-up for intermittent (non-always-on)
+// hosts. When such a host reconnects we wait a short settle window,
+// then dispatch a backup for any schedule whose window elapsed while
+// the host was asleep. This is separate from pending_runs: a host that
+// was asleep never fired its local cron, so no pending row exists.
+package http
+
+import (
+	"time"
+)
+
+// scheduleOverdue reports whether a schedule's most recent expected
+// fire is newer than the host's last successful backup — i.e. a window
+// passed with no backup. A nil lastBackup means "never backed up" and
+// is always overdue (provided the cron parses). An unparseable cron is
+// treated as not-overdue so a bad expression can never trigger a
+// surprise dispatch. Uses the same cronParser the agent's scheduler
+// and schedule validation use, so interpretation is identical.
+func scheduleOverdue(cronExpr string, lastBackup *time.Time, now time.Time) bool {
+	sched, err := cronParser.Parse(cronExpr)
+	if err != nil {
+		return false
+	}
+	if lastBackup == nil {
+		return true
+	}
+	next := sched.Next(*lastBackup)
+	return !next.After(now)
+}