Prepare isolated offsite restore and stream large backup transfers

Assistant: codex
Assistant-Model: gpt-6-astra
Assistant-Session: 01a06ecb-456a-71c2-b41e-0755d336e883

tests/test_offsite_restore_boundaries.py

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+import importlib.util
+from pathlib import Path
+import tempfile
+import unittest
+from unittest.mock import patch
+import sys
+sys.path.insert(0,str(Path(__file__).resolve().parents[1]/'scripts'))
+import verify_nextcloud_offsite_restore as transfer
+import restore_forgejo_offsite_locally as restore
+
+class RestoreBoundary(unittest.TestCase):
+    def test_missing_backup_never_fetches_credentials(self):
+        with tempfile.TemporaryDirectory() as d, patch.object(transfer,'bao') as bao:
+            with self.assertRaises(transfer.LaneError): transfer.run(Path(d)/'absent.zip.age',Path(d)/'stage',{})
+            bao.assert_not_called()
+
+    def test_truncated_backup_never_starts_docker(self):
+        with tempfile.TemporaryDirectory() as d, patch.object(restore.subprocess,'run') as command:
+            p=Path(d)/'fetched.zip';p.write_bytes(b'PK\x03\x04truncated')
+            with self.assertRaises(Exception): restore.run(p,{})
+            command.assert_not_called()