A little better but still broken. I need easier tasks for a while.

src/components/EventDialog.vue

@@ -3,7 +3,7 @@ import { useCalendarStore } from '@/stores/CalendarStore'
 import { ref, computed, watch, onMounted, onUnmounted, nextTick } from 'vue'
 import WeekdaySelector from './WeekdaySelector.vue'
 import Numeric from './Numeric.vue'
-import { addDaysStr } from '@/utils/date'
+import { addDaysStr, getMondayOfISOWeek } from '@/utils/date'
 
 const props = defineProps({
   selection: { type: Object, default: () => ({ startDate: null, dayCount: 0 }) },
@@ -173,11 +173,9 @@ function openEditDialog(payload) {
         // Count valid repeat occurrences (pattern + interval alignment) AFTER the base span
         const interval = event.repeatInterval || 1
         const WEEK_MS = 7 * 86400000
-        const baseBlockStart = new Date(baseStart)
-        baseBlockStart.setDate(baseStart.getDate() - baseStart.getDay())
+        const baseBlockStart = getMondayOfISOWeek(baseStart)
         function isAligned(d) {
-          const blk = new Date(d)
-          blk.setDate(d.getDate() - d.getDay())
+          const blk = getMondayOfISOWeek(d)
           const diff = Math.floor((blk - baseBlockStart) / WEEK_MS)
           return diff % interval === 0
         }