fix(icalendar): Correctly map verbose RRULE keys to standard iCal keys

icalendar.ts

@@ -8,6 +8,27 @@ const CACHE_KEY = "icalendar:lastSync";
 
 console.log(`[iCalendar] Plug script executing at top level (Version ${VERSION})`);
 
+/**
+ * Mapping of verbose RRULE object keys to standard iCalendar shortened keys.
+ */
+const RRULE_KEY_MAP: Record<string, string> = {
+  "frequency": "FREQ",
+  "until": "UNTIL",
+  "count": "COUNT",
+  "interval": "INTERVAL",
+  "bysecond": "BYSECOND",
+  "byminute": "BYMINUTE",
+  "byhour": "BYHOUR",
+  "byday": "BYDAY",
+  "bymonthday": "BYMONTHDAY",
+  "byyearday": "BYYEARDAY",
+  "byweekno": "BYWEEKNO",
+  "bymonth": "BYMONTH",
+  "bysetpos": "BYSETPOS",
+  "wkst": "WKST",
+  "freq": "FREQ", // Just in case
+};
+
 // ============================================================================
 // Utility Functions
 // ============================================================================
@@ -163,7 +184,10 @@ export function expandRecurrences(icsEvent: any, windowDays = 365): any[] {
     } else if (typeof rruleStr === "object" && rruleStr !== null) {
         // Handle object rrule (e.g. from ts-ics) by converting back to string
         cleanRule = Object.entries(rruleStr)
-            .map(([k, v]) => `${k.toUpperCase()}=${v}`)
+            .map(([k, v]) => {
+                const standardKey = RRULE_KEY_MAP[k.toLowerCase()] || k.toUpperCase();
+                return `${standardKey}=${v}`;
+            })
             .join(";");
     } else {
         console.warn(`[iCalendar] Invalid rrule type (${typeof rruleStr}) for event "${icsEvent.summary || "Untitled"}". Treating as non-recurring.`);