fix: anchor floor on re-enable; breaker on scheduled panic; propagate next-run err; reject negative interval; close phantom runs on startup

internal/scheduler/scheduler.go

@@ -19,7 +19,7 @@ const pollInterval = 30 * time.Second
 // run, or one interval after the schedule anchor if it has never completed one.
 func NextRun(interval time.Duration, anchor time.Time, lastFinished *time.Time) time.Time {
 	base := anchor
-	if lastFinished != nil {
+	if lastFinished != nil && lastFinished.After(anchor) {
 		base = *lastFinished
 	}
 	return base.Add(interval)

internal/scheduler/scheduler_test.go

@@ -19,6 +19,12 @@ func TestNextRun(t *testing.T) {
 	if got := NextRun(time.Hour, anchor, &fin); !got.Equal(fin.Add(time.Hour)) {
 		t.Fatalf("recurring: got %v", got)
 	}
+	// Re-enable: anchor is newer than a stale lastFinished from before re-enable →
+	// use anchor, not the stale lastFinished (which would fire immediately/in the past).
+	staleFin := anchor.Add(-2 * time.Hour)
+	if got := NextRun(time.Hour, anchor, &staleFin); !got.Equal(anchor.Add(time.Hour)) {
+		t.Fatalf("re-enable: got %v, want %v", got, anchor.Add(time.Hour))
+	}
 }
 
 func TestDueTaskIDs(t *testing.T) {