fix(assets): only extension-matching buckets contribute a loader_path

The model-base match in get_asset_category_and_relative_path ignored
each bucket's extension set, so a file inside a registered base whose
extension the bucket cannot load (e.g. a .txt uploaded into
model_type:checkpoints) advertised a loader_path that no loader list
would ever resolve, while the tag side of the same stack already
excluded it. Apply the extension check used for backend tags (empty set
accepts any extension), keeping loader_path null exactly when no loader
can resolve the file.

app/assets/services/path_utils.py

@@ -209,8 +209,14 @@ def get_asset_category_and_relative_path(
         return "temp", _compute_relative(fp_abs, temp_base)
 
     # 4) models (check deepest matching base to avoid ambiguity)
+    ext = os.path.splitext(fp_abs)[1].lower()
     best: tuple[int, str, str] | None = None  # (base_len, bucket, rel_inside_bucket)
-    for bucket, bases, _exts in get_comfy_models_folders():
+    for bucket, bases, extensions in get_comfy_models_folders():
+        # A bucket only lists files within its extension set (empty set
+        # accepts any extension), so a bucket that cannot load the file
+        # must not contribute a loader path.
+        if extensions and ext not in extensions:
+            continue
         for b in bases:
             base_abs = os.path.abspath(b)
             if not _check_is_within(fp_abs, base_abs):

tests-unit/assets_test/services/test_path_utils.py

@@ -523,6 +523,42 @@ class TestLoaderPath:
         assert compute_logical_path(str(f)) == "models/not_registered/orphan.bin"
         assert compute_loader_path(str(f)) is None
 
+    def test_extension_mismatch_in_registered_bucket_has_no_loader_path(self, fake_dirs):
+        # Inside a registered bucket, but the bucket's extension set cannot
+        # load it: no model_type tag, and no loader path either.
+        f = fake_dirs["models"] / "notes.txt"
+        f.touch()
+
+        assert compute_logical_path(str(f)) == "models/checkpoints/notes.txt"
+        assert compute_loader_path(str(f)) is None
+
+    def test_shared_base_loader_path_uses_extension_matching_bucket(self, fake_dirs):
+        shared_root = fake_dirs["models"].parent / "unet"
+        shared_root.mkdir()
+        f = shared_root / "wan.gguf"
+        f.touch()
+
+        with patch(
+            "app.assets.services.path_utils.get_comfy_models_folders",
+            return_value=[
+                ("diffusion_models", [str(shared_root)], {".safetensors"}),
+                ("unet_gguf", [str(shared_root)], {".gguf"}),
+            ],
+        ):
+            assert compute_loader_path(str(f)) == "wan.gguf"
+
+    def test_match_all_bucket_provides_loader_path_for_any_extension(self, fake_dirs):
+        custom_root = fake_dirs["models"].parent / "custom_bucket"
+        custom_root.mkdir()
+        f = custom_root / "weights.bin"
+        f.touch()
+
+        with patch(
+            "app.assets.services.path_utils.get_comfy_models_folders",
+            return_value=[("custom_bucket", [str(custom_root)], set())],
+        ):
+            assert compute_loader_path(str(f)) == "weights.bin"
+
     def test_extra_path_model_has_loader_path_but_no_logical_path(self, tmp_path: Path):
         """Registered category base outside models_dir (extra_model_paths style).