fix: three calendar sync bugs

- Fall back to meeting time dates when enrolled terms lack end_date
  (e.g. Fall 2026 before finals are scheduled), so ICS feed holidays
  and university events are no longer silently dropped
- Switch non-holiday university events in ICS feed to date-range query
  instead of term_id filter, matching the holiday fix from ce8d29b
- Assign missing registration_event local var in detect_term_dates;
  undefined reference was raising NoMethodError on every nightly sync,
  silently caught, so term dates were never auto-populated
- Fix cancel_events to also destroy merged records ("merged:A+N") when
  a constituent root UID arrives as CANCELLED from 25live

Author: jaspermayone

app/controllers/calendars_controller.rb

@@ -182,10 +182,8 @@ def add_university_events(cal)
     enrolled_term_ids = @courses.map(&:term_id).compact.uniq
     return if enrolled_term_ids.empty?
 
-    terms = Term.where(id: enrolled_term_ids).where.not(start_date: nil).where.not(end_date: nil)
-    if terms.any?
-      min_date = terms.minimum(:start_date)
-      max_date = terms.maximum(:end_date)
+    min_date, max_date = holiday_date_range_for_terms(enrolled_term_ids)
+    if min_date && max_date
       UniversityCalendarEvent.holidays.in_date_range(min_date, max_date).find_each do |event|
         add_university_event_to_calendar(cal, event, force_all_day: true)
       end
@@ -197,11 +195,28 @@ def add_university_events(cal)
     categories = (user_config.university_event_categories || []) - [ "holiday" ]
     return if categories.empty?
 
-    UniversityCalendarEvent.by_categories(categories).where(term_id: enrolled_term_ids).find_each do |event|
-      add_university_event_to_calendar(cal, event)
+    if min_date && max_date
+      UniversityCalendarEvent.by_categories(categories).in_date_range(min_date, max_date).find_each do |event|
+        add_university_event_to_calendar(cal, event)
+      end
     end
   end
 
+  # Returns [min_date, max_date] for the holiday query range.
+  # Prefers term start/end dates; falls back to meeting time dates when terms
+  # lack end_date (e.g. Fall 2026 before finals are scheduled).
+  def holiday_date_range_for_terms(enrolled_term_ids)
+    terms = Term.where(id: enrolled_term_ids).where.not(start_date: nil).where.not(end_date: nil)
+    if terms.any?
+      return [ terms.minimum(:start_date), terms.maximum(:end_date) ]
+    end
+
+    meeting_times = @courses.flat_map { |c| c.meeting_times.to_a }
+    min = meeting_times.filter_map(&:start_date).min
+    max = meeting_times.filter_map(&:end_date).max
+    [ min, max ]
+  end
+
   def add_university_event_to_calendar(cal, event, force_all_day: false)
     cal.event do |e|
       is_all_day = force_all_day || event.all_day || event.category == "holiday"

app/models/university_calendar_event.rb

@@ -102,6 +102,9 @@ def self.detect_term_dates(year, season)
                                .select { |event| schedule_available_summary?(event.summary) }
                                .min_by(&:start_time)
 
+    registration_event = matching_events
+                         .select { |event| registration_summary?(event.summary) }
+                         .min_by(&:start_time)
     estimated_schedule_available_date = registration_event&.start_time&.to_date&.-(14)
 
     finals_period_event = matching_events

app/services/university_calendar_ics_service.rb

@@ -105,12 +105,21 @@ def cancel_events(uids, stats)
 
     uids.each do |uid|
       event = @existing_events_by_uid&.[](uid)
+
+      # If no direct match, check whether this UID is the root of a merged record
+      # (stored as "merged:<uid>+<count>"). Non-root constituent UIDs of a merged
+      # event are not stored, so only the root cancellation triggers cleanup here.
+      if event.nil? && @existing_events_by_uid
+        merged_prefix = "merged:#{uid}+"
+        _key, event = @existing_events_by_uid.find { |k, _v| k.start_with?(merged_prefix) }
+      end
+
       next unless event
 
-      Rails.logger.info("Removing CANCELLED ICS event: #{event.summary} (#{uid})")
+      Rails.logger.info("Removing CANCELLED ICS event: #{event.summary} (#{uid} -> #{event.ics_uid})")
       stats[:changed_categories] << event.category if event.category.present?
       event.destroy
-      @existing_events_by_uid.delete(uid)
+      @existing_events_by_uid.delete(event.ics_uid)
       stats[:cancelled] += 1
     end
   end