fix(09): IN-02 extract shared resolveFinalRrule helper to deduplicate the update/create RRULE decision tree

apps/api/src/broker/outboxWorker.ts

@@ -143,6 +143,56 @@ export function assembleRruleString(
   return s;
 }
 
+/**
+ * IN-02: shared RRULE-resolution decision tree for the update and create branches.
+ *
+ * The two branches differ only in the SOURCE of `preservedRrule` (the update branch
+ * re-reads it from calendarEvents.rawVevent; the create branch reads the
+ * `_preservedRrule` payload field threaded by the edit-as-move route). The precedence
+ * logic is identical and was previously copy-pasted, risking drift between the two
+ * copies of the RFC-5545 bound-strip (`;(UNTIL|COUNT)=` removal) — see Pitfall 3.
+ *
+ * Precedence:
+ *   1. Explicit recurrence on the payload wins (recurrence:'none' clears the RRULE).
+ *   2. Else, if a preserved RRULE exists and the payload changes only the bound
+ *      (UNTIL/COUNT), strip the preserved RRULE's existing bound and re-apply the new
+ *      one — never naive-concatenate (would produce a double-UNTIL/COUNT).
+ *   3. Else fall back to the payload's preset (rruleFromPayload), or the preserved
+ *      RRULE unchanged when no bound change was requested.
+ */
+function resolveFinalRrule(
+  fields: OutboxPayloadFields,
+  hasExplicitRecurrence: boolean,
+  rruleFromPayload: string | undefined,
+  preservedRrule: string | undefined,
+): string | undefined {
+  if (hasExplicitRecurrence) {
+    // Explicit recurrence wins — recurrence:'none' yields undefined (no RRULE emitted)
+    return rruleFromPayload
+      ? assembleRruleString(
+          rruleFromPayload,
+          fields.recurrenceUntil,
+          fields.recurrenceCount,
+          fields.allDay,
+        )
+      : undefined;
+  }
+  if (preservedRrule) {
+    if (fields.recurrenceUntil || fields.recurrenceCount !== undefined) {
+      // Bound change only: strip existing UNTIL/COUNT, then re-apply the new bound (Pitfall 3)
+      const strippedPreset = preservedRrule.replace(/;(UNTIL|COUNT)=[^;]*/g, '');
+      return assembleRruleString(
+        strippedPreset,
+        fields.recurrenceUntil,
+        fields.recurrenceCount,
+        fields.allDay,
+      );
+    }
+    return preservedRrule;
+  }
+  return rruleFromPayload;
+}
+
 // ── Drain concurrency guard (CR-05) ──────────────────────────────────────────
 
 /**
@@ -422,33 +472,13 @@ async function dispatchRow(row: OutboxRow): Promise<DispatchResult> {
     // concatenate onto `FREQ=WEEKLY;BYDAY=...` which would produce double-UNTIL.
     // WR-01 note: preservedRrule is only set when !hasExplicitRecurrence (see above),
     // so the hasExplicitRecurrence branch always takes precedence over preserved RRULE.
-    let finalRruleString: string | undefined;
+    // IN-02: shared decision tree extracted to resolveFinalRrule (mirrored in create branch).
-    if (hasExplicitRecurrence) {
+    const finalRruleString = resolveFinalRrule(
-      // Explicit recurrence wins — recurrence:'none' yields undefined (no RRULE emitted)
+      fields,
-      finalRruleString = rruleFromPayload
+      hasExplicitRecurrence,
-        ? assembleRruleString(
       rruleFromPayload,
-            fields.recurrenceUntil,
+      preservedRrule,
-            fields.recurrenceCount,
-            fields.allDay,
-          )
-        : undefined;
-    } else if (preservedRrule) {
-      if (fields.recurrenceUntil || fields.recurrenceCount !== undefined) {
-        // Series edit with bound change only: strip existing UNTIL/COUNT, then re-apply
-        const strippedPreset = preservedRrule.replace(/;(UNTIL|COUNT)=[^;]*/g, '');
-        finalRruleString = assembleRruleString(
-          strippedPreset,
-          fields.recurrenceUntil,
-          fields.recurrenceCount,
-          fields.allDay,
     );
-      } else {
-        finalRruleString = preservedRrule;
-      }
-    } else {
-      finalRruleString = rruleFromPayload;
-    }
 
     const { icsString } = buildVeventString({
       uid: row.uid,
@@ -520,33 +550,13 @@ async function dispatchRow(row: OutboxRow): Promise<DispatchResult> {
     // CR-01: an explicit recurrence preset wins over _preservedRrule (deliberate user choice).
     // recurrence:'none' explicitly clears any RRULE — including when _preservedRrule is present.
     // If no explicit recurrence, fall back to _preservedRrule (edit-as-move RRULE carry-through).
-    let finalRruleString: string | undefined;
+    // IN-02: shared decision tree extracted to resolveFinalRrule (mirrored in update branch).
-    if (hasExplicitRecurrence) {
+    const finalRruleString = resolveFinalRrule(
-      // Explicit recurrence wins — recurrence:'none' yields undefined (no RRULE emitted)
+      fields,
-      finalRruleString = rruleFromPayload
+      hasExplicitRecurrence,
-        ? assembleRruleString(
       rruleFromPayload,
-            fields.recurrenceUntil,
+      preservedRrule,
-            fields.recurrenceCount,
-            fields.allDay,
-          )
-        : undefined;
-    } else if (preservedRrule) {
-      if (fields.recurrenceUntil || fields.recurrenceCount !== undefined) {
-        // Bound change on preserved RRULE: strip existing UNTIL/COUNT first (Pitfall 3)
-        const strippedPreset = preservedRrule.replace(/;(UNTIL|COUNT)=[^;]*/g, '');
-        finalRruleString = assembleRruleString(
-          strippedPreset,
-          fields.recurrenceUntil,
-          fields.recurrenceCount,
-          fields.allDay,
     );
-      } else {
-        finalRruleString = preservedRrule;
-      }
-    } else {
-      finalRruleString = rruleFromPayload;
-    }
 
     const { icsString } = buildVeventString({
       uid: row.uid,