Added max list size circumvention for file transfers between sites.

SharepointToolbox/Services/BulkMemberService.cs

@@ -64,6 +64,7 @@ public class BulkMemberService : IBulkMemberService
                 return;
             }
         }
+        catch (OperationCanceledException) { throw; }
         catch (Exception ex)
         {
             Log.Warning("Graph API failed for {GroupUrl}, falling back to CSOM: {Error}",
@@ -83,7 +84,7 @@ public class BulkMemberService : IBulkMemberService
     {
         // Resolve user by email
         var user = await graphClient.Users[email].GetAsync(cancellationToken: ct);
-        if (user == null)
+        if (user?.Id == null)
             throw new InvalidOperationException($"User not found: {email}");
 
         var userRef = $"https://graph.microsoft.com/v1.0/directoryObjects/{user.Id}";
@@ -138,13 +139,16 @@ public class BulkMemberService : IBulkMemberService
                         }
                     }
                 }
-                catch { /* not a group-connected site */ }
+                catch (OperationCanceledException) { throw; }
+                catch (Exception ex) { Log.Debug("Group lookup not available for {SiteUrl}: {Error}", siteUrl, ex.Message); }
             }
 
             return null;
         }
-        catch
+        catch (OperationCanceledException) { throw; }
+        catch (Exception ex)
         {
+            Log.Debug("Could not resolve M365 group ID for {SiteUrl}: {Error}", siteUrl, ex.Message);
             return null;
         }
     }