fix: support staged imports on Docker bind mounts

ingestion/guided_imports.py

@@ -1,6 +1,7 @@
 """Safe discovery of local source documents for the guided import workflow."""
 
 import ctypes
+import errno
 import os
 import stat
 from contextlib import contextmanager
@@ -159,19 +160,35 @@ def _validate_name(name: str) -> None:
 
 
 def _rename_without_replacement(name: str, source_fd: int, destination_fd: int) -> None:
-    # The supported Docker runtime is Linux. Fail closed if atomic no-replace
-    # rename is unavailable instead of falling back to a check-then-replace race.
+    # Use the Linux atomic no-replace rename where the mounted filesystem supports
+    # it. Docker Desktop bind mounts can reject that flag, so preserve the same
+    # no-overwrite guarantee by linking before removing the source.
     try:
-        rename = ctypes.CDLL(None).renameat2
+        library = ctypes.CDLL(None, use_errno=True)
+        rename = library.renameat2
     except AttributeError:
-        raise ParseError("UNREADABLE_FILE") from None
+        rename = None
+    if rename is None:
+        _link_then_unlink(name, source_fd, destination_fd)
+        return
     rename.argtypes = [ctypes.c_int, ctypes.c_char_p, ctypes.c_int, ctypes.c_char_p, ctypes.c_uint]
     rename.restype = ctypes.c_int
     encoded_name = os.fsencode(name)
-    if rename(source_fd, encoded_name, destination_fd, encoded_name, 1) != 0:  # RENAME_NOREPLACE
-        raise ParseError("UNREADABLE_FILE")
+    if rename(source_fd, encoded_name, destination_fd, encoded_name, 1) == 0:  # RENAME_NOREPLACE
+        return
+    if ctypes.get_errno() in {errno.EINVAL, errno.ENOSYS, errno.EOPNOTSUPP}:
+        _link_then_unlink(name, source_fd, destination_fd)
+        return
+    raise ParseError("UNREADABLE_FILE")
 
 
+def _link_then_unlink(name: str, source_fd: int, destination_fd: int) -> None:
+    try:
+        os.link(name, name, src_dir_fd=source_fd, dst_dir_fd=destination_fd, follow_symlinks=False)
+        os.unlink(name, dir_fd=source_fd)
+    except OSError:
+        raise ParseError("UNREADABLE_FILE") from None
+
 def _move_file(name: str, source: str | None, destination: str | None, *, overwrite=False) -> None:
     _validate_name(name)
     with _directory(source) as source_fd, _directory(destination) as destination_fd: