From c7ce0db4fa83c5981d4d74e6c906465ccf3d2279 Mon Sep 17 00:00:00 2001
From: ai-ag2026 <261867348+ai-ag2026@users.noreply.github.com>
Date: Fri, 10 Jul 2026 06:26:30 +0200
Subject: [PATCH] Handle unsupported ownership transfer in atomic writes

---
 api/paths.py                             | 13 ++++++++++++-
 tests/test_5774b_atomic_config_writes.py | 11 +++++++++--
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/api/paths.py b/api/paths.py
index 2fad3194..7254db26 100644
--- a/api/paths.py
+++ b/api/paths.py
@@ -144,7 +144,18 @@ def _atomic_write_text(path: Path, text: str, *, encoding: str = "utf-8") -> Non
         if existing_stat is not None and hasattr(os, "fchown"):
             try:
                 os.fchown(fd, existing_stat.st_uid, existing_stat.st_gid)
-            except (PermissionError, NotImplementedError):
+            except (OSError, NotImplementedError) as exc:
+                unsupported_ownership_errnos = {
+                    errno.EINVAL,
+                    errno.ENOSYS,
+                    errno.ENOTSUP,
+                }
+                if (
+                    isinstance(exc, OSError)
+                    and not isinstance(exc, PermissionError)
+                    and exc.errno not in unsupported_ownership_errnos
+                ):
+                    raise
                 os.close(fd)
                 owns_fd = False
                 os.unlink(tmp)
diff --git a/tests/test_5774b_atomic_config_writes.py b/tests/test_5774b_atomic_config_writes.py
index a4200a3a..bb0f06d5 100644
--- a/tests/test_5774b_atomic_config_writes.py
+++ b/tests/test_5774b_atomic_config_writes.py
@@ -99,15 +99,22 @@ def test_atomic_write_preserves_existing_group(tmp_path: Path) -> None:
 
 
 @pytest.mark.skipif(not hasattr(os, "fchown"), reason="POSIX ownership semantics")
+@pytest.mark.parametrize(
+    "failure",
+    [
+        PermissionError("simulated ownership denial"),
+        OSError(errno.EINVAL, "simulated unsupported ownership transfer"),
+    ],
+)
 def test_fchown_denial_falls_back_without_temp_debris(
-    tmp_path: Path, monkeypatch
+    tmp_path: Path, monkeypatch, failure: OSError
 ) -> None:
     """A writer unable to transfer ownership must keep the old inode contract."""
     target = tmp_path / "config.yaml"
     target.write_text("old: true\n", encoding="utf-8")
 
     def _deny_fchown(*_args) -> None:
-        raise PermissionError("simulated ownership denial")
+        raise failure
 
     monkeypatch.setattr(os, "fchown", _deny_fchown)