Harden canonical publication against races

tests/test_rendering.py

@@ -4,6 +4,7 @@ import contextlib
 import hashlib
 import io
 import json
+import os
 import shutil
 import tempfile
 import unittest
@@ -302,6 +303,49 @@ class DocForgeRenderingTests(unittest.TestCase):
             self.assertEqual(committed_before, committed_output.read_bytes())
             self.assertEqual("current", service.status("manual")["state"])
 
+    def test_manual_and_preview_publication_fsync_their_directories(self) -> None:
+        with tempfile.TemporaryDirectory() as directory:
+            root = self.copy_fixture("alpha", Path(directory))
+            project = Project.open(root)
+            changesets = ChangesetStore(project, "alpha-editor")
+            service = RenderService(project, changesets)
+            proposal = changesets.create("durable-preview")
+            proposal = changesets.propose_update(
+                changeset_id="durable-preview",
+                expected_changeset_hash=str(proposal["changeset_hash"]),
+                node_id="guide.workflow",
+                expected_content_hash=self.node_hash(project, "guide.workflow"),
+                metadata={"summary": "Durable preview output."},
+                content=None,
+                relationship_changes=[],
+                rationale="Exercise durable preview publication.",
+            )
+            del proposal
+            real_fsync = os.fsync
+            fsynced_directories: set[Path] = set()
+
+            def record_fsync(descriptor: int) -> None:
+                try:
+                    path = Path(os.readlink(f"/proc/self/fd/{descriptor}"))
+                    if path.is_dir():
+                        fsynced_directories.add(path)
+                except OSError:
+                    pass
+                real_fsync(descriptor)
+
+            with mock.patch(
+                "docforge._fs_safety.os.fsync",
+                side_effect=record_fsync,
+            ):
+                service.render("manual")
+                service.preview("durable-preview", "manual")
+
+            self.assertIn(root / ".docforge/rendered", fsynced_directories)
+            self.assertIn(
+                root / ".docforge/previews/durable-preview",
+                fsynced_directories,
+            )
+
     def test_failed_and_mid_input_renders_preserve_previous_outputs(self) -> None:
         with tempfile.TemporaryDirectory() as directory:
             root = self.copy_fixture("alpha", Path(directory))