fix(pending-delete): drop the staging container with its last batch (#1145)

Deleting a folder that holds models answered "A deletion is still pending inside
this folder. Wait for the undo window to expire." even though nothing was staged
and no window was running. `.lm-pending-delete` is only a container: the purge,
the undo and the staging rollback all removed the batch dir inside it and left the
container behind, and the folder manifest matched the directory *name* alone. Any
folder where a model had ever been deleted with the undo window was therefore
undeletable for good, and the same name match refused folder renames.

* `staging_dir_has_content()` is the shared answer to "is there still a batch
  here?": an empty container is a leftover, a quarantined batch (`*.orphaned`) is
  preserved data and still counts, and an unreadable directory counts too — never
  delete over something that could not be listed.
* The container is removed with its last batch (purge, undo, staging rollback,
  merged-loser cleanup). `rmdir` only ever succeeds on an empty directory, and the
  path is checked to really be a `.lm-pending-delete`, so a model folder is never
  at risk.
* A manifest-less batch dir with nothing in it is a crash leftover between
  `makedirs` and the manifest write: it is dropped instead of quarantined, which
  would have left an empty container that blocks deletion just the same.

Verified: purge, undo and the empty-manifest-less sweep all leave no container
behind, the container survives while another batch is staged, and an empty one no
longer blocks folder delete or rename while a real (or quarantined) batch still
does. 3818 backend tests pass.

py/services/model_file_service.py

@@ -12,7 +12,10 @@ from ..utils.recipes_paths import path_is_or_contains_recipes_dir
 from ..utils.sidecar_paths import is_centralized, resolve_centralized_dir_for_dir
 from ..services.settings_manager import get_settings_manager
 from ..services.model_lifecycle_service import _require_path_in_library_roots
-from ..services.pending_delete_service import PENDING_DELETE_DIR_NAME
+from ..services.pending_delete_service import (
+    PENDING_DELETE_DIR_NAME,
+    staging_dir_has_content,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -881,7 +884,12 @@ class ModelMoveService:
         excluded_paths = self._excluded_model_paths()
 
         for dirpath, dirnames, filenames in os.walk(absolute_path):
-            if PENDING_DELETE_DIR_NAME in dirnames:
+            # The container alone means nothing: an empty `.lm-pending-delete`
+            # is a leftover from a purge, an undo or a failed staging, and
+            # treating it as pending made the folder undeletable for good.
+            if PENDING_DELETE_DIR_NAME in dirnames and staging_dir_has_content(
+                os.path.join(dirpath, PENDING_DELETE_DIR_NAME)
+            ):
                 pending_delete_job = True
 
             for name in dirnames:
@@ -1072,9 +1080,15 @@ class ModelMoveService:
 
     @staticmethod
     def _has_pending_delete_job(absolute_path: str) -> bool:
-        """Return True when a staged-delete batch lives inside the subtree."""
-        for _dirpath, dirnames, _filenames in os.walk(absolute_path):
-            if PENDING_DELETE_DIR_NAME in dirnames:
+        """Return True when a staged-delete batch lives inside the subtree.
+
+        An empty ``.lm-pending-delete`` container does not count: it is a
+        leftover, not a batch, and a rename must not be refused because of one.
+        """
+        for dirpath, dirnames, _filenames in os.walk(absolute_path):
+            if PENDING_DELETE_DIR_NAME in dirnames and staging_dir_has_content(
+                os.path.join(dirpath, PENDING_DELETE_DIR_NAME)
+            ):
                 return True
         return False