fix: fall back to additional_data when extracting @odata.deltaLink

Matches the .NET SDK's PageIterator, which checks AdditionalData
before the strongly-typed OdataDeltaLink property. A custom
constructor_callable model that doesn't declare odata_delta_link would
otherwise silently lose the delta link, same failure mode as before.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: DPGrev

src/msgraph_core/tasks/page_iterator.py

@@ -83,9 +83,7 @@ def __init__(
         self._next_link = response.get('odata_next_link', '') if isinstance(
             response, dict
         ) else getattr(response, 'odata_next_link', '')
-        self._delta_link = response.get('@odata.deltaLink', '') if isinstance(
-            response, dict
-        ) else getattr(response, 'odata_delta_link', '')
+        self._delta_link = self._extract_delta_link(response)
 
         if page is not None:
             self.current_page = page
@@ -151,14 +149,32 @@ async def next(self) -> Optional[PageResult]:
         next_link = response.odata_next_link if response and hasattr(
             response, 'odata_next_link'
         ) else None
-        delta_link = response.odata_delta_link if response and hasattr(
-            response, 'odata_delta_link'
-        ) else None
+        delta_link = self._extract_delta_link(response) if response else None
         if delta_link:
             self._delta_link = delta_link
         value = response.value if response and hasattr(response, 'value') else None
         return PageResult(odata_next_link=next_link, value=value)
 
+    @staticmethod
+    def _extract_delta_link(response: Union[T, dict, object]) -> str:
+        """
+        Extracts the '@odata.deltaLink' from a response.
+        Checks the additional data bag first (for models that do not
+        explicitly declare the field), then falls back to the typed
+        'odata_delta_link' attribute.
+        Args:
+            response (Union[T, dict, object]): The response to extract the
+            delta link from.
+        Returns:
+            str: The delta link, or an empty string if none is present.
+        """
+        if isinstance(response, dict):
+            return response.get('@odata.deltaLink', '')
+        additional_data = getattr(response, 'additional_data', None)
+        if additional_data and additional_data.get('@odata.deltaLink'):
+            return additional_data.get('@odata.deltaLink')
+        return getattr(response, 'odata_delta_link', '')
+
     @staticmethod
     def convert_to_page(response: Union[T, list, object]) -> PageResult:
         """

tests/tasks/test_page_iterator.py

@@ -125,6 +125,39 @@ async def test_delta_link_updated_from_final_page():
     assert page_iterator.delta_link == 'https://graph.microsoft.com/v1.0/delta?token=final'
 
 
+class _CustomPage:  # pylint: disable=too-few-public-methods
+    """A page response whose model does not declare 'odata_delta_link' and
+    instead carries it in the additional data bag, like a Kiota-generated
+    collection response that doesn't model the deltaLink property."""
+
+    def __init__(self, value, odata_next_link=None, additional_data=None):
+        self.value = value
+        self.odata_next_link = odata_next_link
+        self.additional_data = additional_data or {}
+
+
+@pytest.mark.asyncio
+async def test_delta_link_falls_back_to_additional_data():
+    """Reproduces the gap where a model without a typed 'odata_delta_link'
+    attribute stores the delta link in additional_data instead."""
+    first_page = PageResult(odata_next_link='https://graph.microsoft.com/v1.0/next', value=[1, 2])
+    final_page = _CustomPage(
+        value=[3, 4],
+        additional_data={'@odata.deltaLink': 'https://graph.microsoft.com/v1.0/delta?token=final'},
+    )
+
+    adapter = Mock()
+    adapter.send_async = AsyncMock(return_value=final_page)
+
+    page_iterator = PageIterator(first_page, adapter)
+
+    items = []
+    await page_iterator.iterate(lambda item: items.append(item) or True)
+
+    assert items == [1, 2, 3, 4]
+    assert page_iterator.delta_link == 'https://graph.microsoft.com/v1.0/delta?token=final'
+
+
 @pytest.mark.asyncio
 async def test_iterate():
     # Mock the next method to return None after the first call