Harden canonical publication against races

tests/test_incremental_cache.py

@@ -2,9 +2,11 @@ from __future__ import annotations
 
 import hashlib
 import os
+import stat
 import tempfile
 import unittest
 from pathlib import Path
+from unittest import mock
 
 from docforge.errors import DocForgeError
 from docforge.incremental import (
@@ -97,6 +99,24 @@ class ExtractionCacheBoundsTests(unittest.TestCase):
                     )
                 )
 
+    def test_cache_publication_fsyncs_the_parent_directory(self) -> None:
+        with tempfile.TemporaryDirectory() as directory:
+            path = Path(directory) / "extractions.json"
+            real_fsync = os.fsync
+            fsynced_modes: list[int] = []
+
+            def record_fsync(descriptor: int) -> None:
+                fsynced_modes.append(os.fstat(descriptor).st_mode)
+                real_fsync(descriptor)
+
+            with mock.patch(
+                "docforge._fs_safety.os.fsync",
+                side_effect=record_fsync,
+            ):
+                write_extraction_cache(path, self.cache(), max_bytes=1_000, max_sources=2)
+
+            self.assertTrue(any(stat.S_ISDIR(mode) for mode in fsynced_modes))
+
 
 if __name__ == "__main__":
     unittest.main()