feat: support EXDATE, DATE+DURATION, and weekly day inference

- Handle DATE+DURATION all-day events by computing end_date from
  duration
- Add PUSH/POP-OMIT-CONTEXT and OMIT/SKIP support for EXDATE in
  daily/weekly rendering
- Adjust UNTIL date when local time of UNTIL timestamp precedes event
  start time
- Default weekly RRULE to event's own weekday when BYDAY list is empty
- Remove EXDATE check from complex-recurrence guard (handled via OMIT
  now)
- Add timedesc_wd_to_ical weekday conversion utility
- Remove verbose EXDATE debug logging
- Fix minor newline in file processing log message

bin/remind.ml

@@ -67,12 +67,24 @@ let add_interval_daily b (d : simple_daily) =
   let n = Option.value ~default:1 d.interval in
   Buffer.add_string b (spf "*%d " n)
 
+(** Adjust an UNTIL date: if the event has a start time and the local time of the UNTIL timestamp is strictly before
+    that start time, the last valid occurrence is on the previous day. *)
+let until_date_adjusted (until_ts : Timedesc.t) (event_time : Timedesc.Time.t option) : Timedesc.Date.t =
+  let until_date = Timedesc.date until_ts in
+  match event_time with
+  | None -> until_date
+  | Some evt_t ->
+      let until_t = Timedesc.time until_ts in
+      let cmp = Timedesc.Span.compare (Timedesc.Time.to_span until_t) (Timedesc.Time.to_span evt_t) in
+      if cmp < 0 then Timedesc.Date.add ~days:(-1) until_date else until_date
+
 let add_until b rem (w : simple_weekly) =
   match w.count_or_until with
   | None -> ()
   | Some (`Until d) ->
       let ts = timedesc_of_utc_or_timestamp_local d in
-      Buffer.add_string b (spf "UNTIL %s " (Timedesc.Date.to_rfc3339 (Timedesc.date ts)))
+      let date = until_date_adjusted ts rem.time in
+      Buffer.add_string b (spf "UNTIL %s " (Timedesc.Date.to_rfc3339 date))
   | Some (`Count count) ->
       let wd = Timedesc.Date.weekday rem.date in
       let wd_int = Timedesc.Utils.tm_int_of_weekday wd in
@@ -90,7 +102,8 @@ let add_until_daily b rem (d : simple_daily) =
   | None -> ()
   | Some (`Until dt) ->
       let ts = timedesc_of_utc_or_timestamp_local dt in
-      Buffer.add_string b (spf "UNTIL %s " (Timedesc.Date.to_rfc3339 (Timedesc.date ts)))
+      let date = until_date_adjusted ts rem.time in
+      Buffer.add_string b (spf "UNTIL %s " (Timedesc.Date.to_rfc3339 date))
   | Some (`Count count) ->
       let iv = Option.value ~default:1 d.interval in
       let until = Timedesc.Date.add ~days:((count - 1) * iv) rem.date in
@@ -110,10 +123,32 @@ let add_through b = function
 
 let add_msg b summary = Buffer.add_string b (spf " MSG %s\n" summary)
 
+let date_of_date_or_datetime (d : Icalendar.date_or_datetime) : Timedesc.Date.t =
+  match d with
+  | `Date (year, month, day) -> Timedesc.Date.Ymd.make_exn ~year ~month ~day
+  | `Datetime ts -> Timedesc.date (timedesc_of_timestamp ts)
+
+let add_omit b (d : Icalendar.date_or_datetime) =
+  let date = date_of_date_or_datetime d in
+  let day = Timedesc.Date.day date in
+  let month = string_of_month (month_of_int (Timedesc.Date.month date)) in
+  let year = Timedesc.Date.year date in
+  Buffer.add_string b (spf "OMIT %d %s %d\n" day month year)
+
+let add_omit_context b exdates =
+  if exdates <> [] then begin
+    Buffer.add_string b "PUSH-OMIT-CONTEXT\n";
+    List.iter (add_omit b) exdates
+  end
+
+let close_omit_context b exdates = if exdates <> [] then Buffer.add_string b "POP-OMIT-CONTEXT\n"
+let add_skip b exdates = if exdates <> [] then Buffer.add_string b "SKIP "
+
 (* ── rendering ────────────────────────────────────────────────── *)
 
 let render_daily rem (d : simple_daily) =
   let b = Buffer.create 256 in
+  add_omit_context b rem.exdate;
   add_rem b;
   add_info b rem.original_uuid;
   add_source b rem.source;
@@ -121,13 +156,16 @@ let render_daily rem (d : simple_daily) =
   Buffer.add_char b ' ';
   add_interval_daily b d;
   add_until_daily b rem d;
+  add_skip b rem.exdate;
   add_at b rem.time;
   add_duration b rem.duration;
   add_msg b rem.summary;
+  close_omit_context b rem.exdate;
   Buffer.contents b
 
 let render_weekly rem (w : simple_weekly) =
   let b = Buffer.create 256 in
+  add_omit_context b rem.exdate;
   List.iter
     (fun wd ->
       add_rem b;
@@ -138,10 +176,12 @@ let render_weekly rem (w : simple_weekly) =
       Buffer.add_char b ' ';
       add_interval b w;
       add_until b rem w;
+      add_skip b rem.exdate;
       add_at b rem.time;
       add_duration b rem.duration;
       add_msg b rem.summary)
     w.byday;
+  close_omit_context b rem.exdate;
   Buffer.contents b
 
 let render_single rem =