fix(files): isolate archive workers and make handoff event driven

tests/test_archive_performance.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from contextlib import closing
 from io import BytesIO
 from pathlib import Path
 import random
@@ -204,24 +205,16 @@ class NativeArchivePerformanceTests(unittest.TestCase):
                 "govoplan_files.backend.storage.archives.native_zip_library",
                 return_value=proxy,
             ),
-            patch(
-                "govoplan_files.backend.storage.archives.create_file_asset",
-                side_effect=FileStorageError("Destination failure"),
-            ),
         ):
             with self.assertRaisesRegex(FileStorageError, "Destination failure"):
-                extract_archive_upload(
-                    object(),
-                    tenant_id="tenant",
-                    owner_type="user",
-                    owner_id="user",
-                    user_id="user",
-                    archive_data=self.archive,
-                    filename="archive.zip",
-                    folder="",
-                    campaign_id=None,
-                    password="fixture-only",
-                )
+                # This unit test owns the native handle locally; public imports
+                # now own it in a fresh child (covered by worker cleanup tests).
+                with closing(_read_selected_zip_members(
+                    self.archive, selected_files=set(self.contents), password="fixture-only",
+                    max_file_bytes=100_000, max_total_bytes=100_000,
+                )) as members:
+                    next(members)
+                    raise FileStorageError("Destination failure")
         close.assert_called_once()
 
     def test_native_read_enforces_actual_member_and_total_limits(self):