perf(import): reuse auto-created groups across import chunks

test/mv/membership/import/import_runner_test.exs

@@ -3,6 +3,24 @@ defmodule Mv.Membership.Import.ImportRunnerTest do
 
   alias Mv.Membership.Import.ImportRunner
 
+  describe "carry_groups_forward/2" do
+    test "replaces import_state groups_found with the chunk's grown snapshot" do
+      import_state = %{groups_found: [%{id: "1", name: "A"}]}
+      chunk_result = %{groups_found: [%{id: "1", name: "A"}, %{id: "2", name: "B"}]}
+
+      assert ImportRunner.carry_groups_forward(import_state, chunk_result) == %{
+               groups_found: [%{id: "1", name: "A"}, %{id: "2", name: "B"}]
+             }
+    end
+
+    test "leaves import_state unchanged when the chunk result omits groups_found" do
+      import_state = %{groups_found: [%{id: "1", name: "A"}], other: :kept}
+      chunk_result = %{inserted: 1}
+
+      assert ImportRunner.carry_groups_forward(import_state, chunk_result) == import_state
+    end
+  end
+
   describe "read_file_entry/2" do
     test "returns {:ok, content} for a readable file" do
       path =