[opcreds] Fix LEAVE event on RemoveFabric (#18434)

* [opcreds] Fix LEAVE event on RemoveFabric

LEAVE event is not emitted on RemoveFabric or factory reset.
There are two reasons for that:
- Removing a fabric causes closing all active ReadHandlers
  for a given fabric, so we must flush the event log before
  that happens.
- There are two listeners for removing a fabric; the one
  that removes ACLs for a given fabric index is executed
  prior to the other one that generates LEAVE event. That
  causes "Accces control: denied" error.

Fix both issues.

* Add comment

src/app/clusters/operational-credentials-server/operational-credentials-server.cpp

@@ -364,8 +364,7 @@ class OpCredsFabricTableDelegate : public chip::FabricTable::Delegate
                        static_cast<unsigned>(fabricIndex));
         fabricListChanged();
 
-        // The Leave event SHOULD be emitted by a Node prior to permanently
-        // leaving the Fabric.
+        // The Leave event SHOULD be emitted by a Node prior to permanently leaving the Fabric.
         for (auto endpoint : EnabledEndpointsWithServerCluster(Basic::Id))
         {
             // If Basic cluster is implemented on this endpoint
@@ -377,6 +376,26 @@ class OpCredsFabricTableDelegate : public chip::FabricTable::Delegate
                 ChipLogError(Zcl, "OpCredsFabricTableDelegate: Failed to record Leave event");
             }
         }
+
+        // Try to send the queued events as soon as possible. If the just emitted leave event won't
+        // be sent this time, it will likely not be delivered at all for the following reasons:
+        // - removing the fabric expires all associated ReadHandlers, so all subscriptions to
+        //   the leave event will be cancelled.
+        // - removing the fabric removes all associated access control entries, so generating
+        //   subsequent reports containing the leave event will fail the access control check.
+        InteractionModelEngine::GetInstance()->GetReportingEngine().ScheduleUrgentEventDeliverySync();
+        EventManagement::GetInstance().FabricRemoved(fabricIndex);
+
+        // Remove access control entries in reverse order (it could be any order, but reverse order
+        // will cause less churn in persistent storage).
+        size_t aclCount = 0;
+        if (Access::GetAccessControl().GetEntryCount(fabricIndex, aclCount) == CHIP_NO_ERROR)
+        {
+            while (aclCount)
+            {
+                (void) Access::GetAccessControl().DeleteEntry(nullptr, fabricIndex, --aclCount);
+            }
+        }
     }
 
     // Gets called when a fabric is loaded into the FabricTable from storage

src/app/server/Server.h

@@ -333,21 +333,6 @@ class Server
                                  static_cast<unsigned>(fabricIndex), err.Format());
                 }
             }
-
-            {
-                // Remove access control entries in reverse order. (It could be
-                // any order, but reverse order will cause less churn in
-                // persistent storage.)
-                size_t count = 0;
-                if (Access::GetAccessControl().GetEntryCount(fabricIndex, count) == CHIP_NO_ERROR)
-                {
-                    while (count)
-                    {
-                        (void) Access::GetAccessControl().DeleteEntry(nullptr, fabricIndex, --count);
-                    }
-                }
-            }
-            app::EventManagement::GetInstance().FabricRemoved(fabricIndex);
         };
 
         void OnFabricRetrievedFromStorage(FabricTable & fabricTable, FabricIndex fabricIndex) override