feat(event-predicates): warn on unhandled recurrence overrides and multiple masters

- Add `warn_unhandled_recurring` collector that emits a warning when
  `RECURRENCE-ID` overrides are present but not yet handled, emitting
  the master event as-is
- Register `warn_unhandled_recurring` in `all_collectors`
- Warn when more than one master event (no `RECURRENCE-ID`) is found for
  a UID in `separate_master_and_recurrence`, using only the first

bin/eventPredicates.ml

@@ -326,8 +326,22 @@ RRULE: (`Weekly, (Some `Until (`Utc (2026-07-01 09:00:00 +00:00))), None, [])
   | Some (_, recurs) -> debug_print_of_recurrence_and_skip ev recurs
   | None -> Ok rem
 
+let warn_unhandled_recurring rem ev : (Remind.rem, error) result =
+  if List.length rem.Remind.recurring > 0 then
+    Printf.eprintf "Warning: RECURRENCE-ID overrides present but not handled (master emitted as-is)\t\t\tUID: %s\n"
+      (Utils.get_uid ev);
+  Ok rem
+
 let all_collectors : collector list =
-  [ collect_uuid; collect_summary; collect_start_end_duration; collect_exdates; yearly_simple_date; simple_recurrence ]
+  [
+    collect_uuid;
+    collect_summary;
+    collect_start_end_duration;
+    collect_exdates;
+    yearly_simple_date;
+    simple_recurrence;
+    warn_unhandled_recurring;
+  ]
 
 let remind_of_event (source : string) (ev : Icalendar.event list) : (Remind.rem, error) result =
   let () = if List.length ev = 0 then failwith "No events provided" in

bin/utils.ml

@@ -182,4 +182,8 @@ let separate_master_and_recurrence (events : Icalendar.event list) : Icalendar.e
   in
   match master_and_recurrences with
   | [], _ -> failwith "No master event found"
-  | master :: _, recurrences -> (master, recurrences)
+  | [ master ], recurrences -> (master, recurrences)
+  | master :: rest, recurrences ->
+      Printf.eprintf "Warning: %d extra master events (no RECURRENCE-ID) for UID: %s — only first used\n"
+        (List.length rest) (get_uid master);
+      (master, recurrences)