fix: skip Xero phone sync for merged companies

apps/workflow/api/xero/reprocess_xero.py

@@ -47,6 +47,12 @@ def sync_xero_phone_methods(company: Company) -> list[str]:
     Returns the normalized numbers that were newly created, so the caller can
     dispatch a call rematch for them.
     """
+    # A merged company's numbers live on the company it was merged into. Its
+    # archived Xero contact keeps the phones (and is still fetched with
+    # include_archived=True), so syncing it would collide with the winner's
+    # rows under the one-number-one-company rule.
+    if company.merged_into_id:
+        return []
     phones = company.raw_json.get("_phones", []) if company.raw_json else []
     if not isinstance(phones, list):
         return []

apps/workflow/tests/test_sync_clients.py

@@ -345,6 +345,28 @@ def test_duplicate_phone_owner_crashes_sync_and_persists_app_error(self) -> None
         self.assertIn("+6421555123", app_error.message)
         self.assertIn("Existing Phone Owner", app_error.message)
 
+    def test_merged_company_phones_are_not_synced(self) -> None:
+        """A merged company's archived Xero contact keeps its phones, but they
+        now belong to the winner — syncing must skip, not collide."""
+        winner = Company.objects.create(
+            name="Winner", xero_last_modified=timezone.now()
+        )
+        ContactMethod.objects.create(
+            company=winner,
+            method_type=ContactMethod.MethodType.PHONE,
+            value="021 555 123",
+        )
+        merged = self._client_with_phone("Merged Loser")
+        merged.merged_into = winner
+        merged.save()
+        before = AppError.objects.count()
+
+        created = sync_xero_phone_methods(merged)  # must not raise
+
+        self.assertEqual(created, [])
+        self.assertEqual(ContactMethod.objects.filter(company=merged).count(), 0)
+        self.assertEqual(AppError.objects.count(), before)
+
     def test_resync_of_existing_number_is_grandfathered(self) -> None:
         """Re-syncing a company's own already-stored number must not raise."""
         owner = self._client_with_phone("Phone Owner")