fix: use deterministic hash for SCHED/WARN function names

Replaces the global sequential counter (sched_1, warn_2, …) with a
polynomial hash of (UUID ^ date), so names are stable across runs and
unique across calendars — eliminating "function redefined" errors when
multiple .rem files are included by Remind.

bin/remind.ml

@@ -80,12 +80,13 @@ let empty =
 
 (* ── alarm rendering ─────────────────────────────────────────── *)
 
-(** Global counter for generating unique WARN/SCHED function names *)
-let alarm_id = ref 0
-
-let next_alarm_id () =
-  incr alarm_id;
-  !alarm_id
+(** Deterministic alarm function name tag derived from the event UID and date. Using both fields ensures uniqueness
+    across calendars (UUID is globally unique) and between a master event and its date-specific overrides (which share
+    the same UUID). *)
+let alarm_hash rem =
+  let key = rem.original_uuid ^ Timedesc.Date.to_rfc3339 rem.date in
+  let h = String.fold_left (fun acc c -> ((acc * 1000003) + Char.code c) land 0x3FFFFFFF) 0 key in
+  spf "%08x" h
 
 (** Convert a Timedesc.Span.t to signed total minutes. Negative = before event; positive = after event. *)
 let span_to_minutes (sp : Timedesc.Span.t) : int =
@@ -141,8 +142,7 @@ let render_alarm (rem : rem) : alarm_rendering =
         | [] -> empty_alarm
         | [ n ] -> { empty_alarm with time_delta = spf "+%d " n }
         | mins ->
-            let id = next_alarm_id () in
-            let name = spf "sched_%d" id in
+            let name = spf "sched_%s" (alarm_hash rem) in
             (* SCHED sequence: most-advance first (most negative), then 0 to stop.
            mins is sorted ascending (closest first), so reverse for SCHED order. *)
             let sched_vals = List.rev_map (fun n -> spf "%d" (-n)) mins @ [ "0" ] in
@@ -155,8 +155,7 @@ let render_alarm (rem : rem) : alarm_rendering =
         | [] -> empty_alarm
         | [ n ] -> { empty_alarm with day_delta = spf "++%d " n }
         | days ->
-            let id = next_alarm_id () in
-            let name = spf "warn_%d" id in
+            let name = spf "warn_%s" (alarm_hash rem) in
             (* WARN sequence: furthest first (days sorted descending), then 0 to stop. *)
             let warn_vals = List.map string_of_int (days @ [ 0 ]) in
             let fset = spf "FSET %s(x) choose(x, %s)\n" name (String.concat ", " warn_vals) in