✨(backend) activate restriction by moving the folder to the tree root

Restriction is structural: the folder physically leaves its parent
so inheritance stops applying without any query-level cut. A
shortcut materializes its origin location. Explicit link reach is
kept and defaults to restricted only when it was inherited.

src/backend/core/models.py

@@ -1541,6 +1541,30 @@ class Item(TreeModel, BaseModel):
                 }
             )
 
+        if self.is_restricted:
+            raise ValidationError(
+                {
+                    "target": ValidationError(
+                        _("A restricted folder cannot be moved"),
+                        code="item_move_restricted",
+                    )
+                }
+            )
+
+        if (
+            self.type == ItemTypeChoices.SHORTCUT
+            and target
+            and str(target.path).startswith(str(self.target.path))
+        ):
+            raise ValidationError(
+                {
+                    "target": ValidationError(
+                        _("A shortcut cannot be moved under its own target"),
+                        code="item_move_shortcut_under_target",
+                    )
+                }
+            )
+
         old_path = self.path
         if target:
             self.path = f"{target.path!s}.{self.id!s}"
@@ -1555,6 +1579,74 @@ class Item(TreeModel, BaseModel):
                 path=RawSQL("%s || subpath(path, nlevel(%s))", (str(self.path), str(old_path)))
             )
 
+    @transaction.atomic
+    def restrict(self, user):
+        """Restrict the folder by detaching it to the tree root behind a shortcut."""
+        item = self._meta.model.objects.select_for_update().get(pk=self.pk)
+
+        if item.type != ItemTypeChoices.FOLDER:
+            raise ValidationError(
+                {
+                    "is_restricted": ValidationError(
+                        _("Only folders can be restricted"),
+                        code="item_restrict_type_folder_only",
+                    )
+                }
+            )
+        if item.is_restricted:
+            raise ValidationError(
+                {
+                    "is_restricted": ValidationError(
+                        _("This folder is already restricted"),
+                        code="item_restrict_already_restricted",
+                    )
+                }
+            )
+        if item.depth == 1:
+            raise ValidationError(
+                {
+                    "is_restricted": ValidationError(
+                        _("A root folder cannot be restricted"),
+                        code="item_restrict_root",
+                    )
+                }
+            )
+        if item.ancestors_deleted_at:
+            raise ValidationError(
+                {
+                    "is_restricted": ValidationError(
+                        _("A deleted folder cannot be restricted"),
+                        code="item_restrict_deleted",
+                    )
+                }
+            )
+
+        parent = item.parent()
+
+        ItemAccess.objects.update_or_create(
+            item=item, user=user, defaults={"role": RoleChoices.OWNER}
+        )
+
+        # The move must run while the flag is still unset: move() refuses
+        # restricted folders
+        item.move(None)
+
+        item.is_restricted = True
+        if item.link_reach is None:
+            item.link_reach = LinkReachChoices.RESTRICTED
+        item.save(update_fields=["is_restricted", "link_reach"])
+
+        self._meta.model.objects.create_child(
+            parent=parent,
+            creator=user,
+            type=ItemTypeChoices.SHORTCUT,
+            target=item,
+            title=item.title,
+        )
+        item.invalidate_nb_accesses_cache()
+
+        return item
+
 
 class MirrorItemTask(BaseModel):
     """Model managing a status for a mirroring task."""

src/backend/core/tests/test_models_items_restricted.py

@@ -3,6 +3,7 @@
 from django.core.exceptions import ValidationError
 
 import pytest
+from lasuite.drf.models.choices import LinkReachChoices
 
 from core import factories, models
 
@@ -93,3 +94,226 @@ def test_models_items_restricted_file_cannot_be_restricted():
     """A file cannot be restricted."""
     with pytest.raises(ValidationError):
         factories.ItemFactory(type=models.ItemTypeChoices.FILE, is_restricted=True)
+
+
+def test_models_items_restricted_restrict_moves_folder_to_root():
+    """Activating restriction moves the folder and its subtree to the tree root."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    folder = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FOLDER)
+    child = factories.ItemFactory(parent=folder, type=models.ItemTypeChoices.FILE)
+
+    folder.restrict(user)
+
+    folder.refresh_from_db()
+    child.refresh_from_db()
+    assert str(folder.path) == str(folder.id)
+    assert str(child.path) == f"{folder.id!s}.{child.id!s}"
+
+
+def test_models_items_restricted_restrict_creates_shortcut():
+    """Activating restriction materializes the origin location with a shortcut."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    folder = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FOLDER)
+
+    folder.restrict(user)
+
+    folder.refresh_from_db()
+    shortcut = folder.shortcut
+    assert shortcut.type == models.ItemTypeChoices.SHORTCUT
+    assert str(shortcut.path) == f"{parent.id!s}.{shortcut.id!s}"
+    assert shortcut.title == folder.title
+    assert shortcut.creator == user
+
+
+def test_models_items_restricted_restrict_sets_flag_and_creates_owner_access():
+    """Activating restriction sets is_restricted and creates an explicit owner access."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    folder = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FOLDER)
+
+    assert not models.ItemAccess.objects.filter(item=folder, user=user).exists()
+
+    folder = folder.restrict(user)
+
+    assert folder.is_restricted is True
+    assert models.ItemAccess.objects.filter(item=folder, user=user, role="owner").exists()
+
+
+def test_models_items_restricted_restrict_keeps_existing_explicit_access():
+    """Activating restriction does not duplicate an existing explicit owner access."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    folder = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FOLDER)
+    factories.UserItemAccessFactory(item=folder, user=user, role="owner")
+
+    folder.restrict(user)
+
+    assert models.ItemAccess.objects.filter(item=folder, user=user, role="owner").count() == 1
+
+
+def test_models_items_restricted_restrict_promotes_existing_lower_access():
+    """Activating restriction promotes an existing lower explicit access to owner."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    folder = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FOLDER)
+    access = factories.UserItemAccessFactory(item=folder, user=user, role="reader")
+
+    folder.restrict(user)
+
+    access.refresh_from_db()
+    assert access.role == models.RoleChoices.OWNER
+
+
+def test_models_items_restricted_restrict_defaults_link_reach():
+    """Activating restriction sets link reach to restricted when none is explicit."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(
+        type=models.ItemTypeChoices.FOLDER,
+        link_reach=LinkReachChoices.PUBLIC,
+        link_role="reader",
+    )
+    folder = factories.ItemFactory(
+        parent=parent,
+        type=models.ItemTypeChoices.FOLDER,
+        link_reach=None,
+    )
+
+    folder = folder.restrict(user)
+
+    assert folder.link_reach == LinkReachChoices.RESTRICTED
+
+
+def test_models_items_restricted_restrict_keeps_explicit_link_reach():
+    """Activating restriction keeps an existing explicit link reach."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    folder = factories.ItemFactory(
+        parent=parent,
+        type=models.ItemTypeChoices.FOLDER,
+        link_reach=LinkReachChoices.AUTHENTICATED,
+    )
+
+    folder = folder.restrict(user)
+
+    assert folder.link_reach == LinkReachChoices.AUTHENTICATED
+
+
+def test_models_items_restricted_restrict_requires_a_folder():
+    """Only folders can be restricted."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    item = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FILE)
+
+    with pytest.raises(ValidationError, match="Only folders can be restricted"):
+        item.restrict(user)
+
+
+def test_models_items_restricted_restrict_rejects_already_restricted():
+    """A restricted folder cannot be restricted again."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    folder = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FOLDER)
+    folder.restrict(user)
+    folder.refresh_from_db()
+
+    with pytest.raises(ValidationError, match="This folder is already restricted"):
+        folder.restrict(user)
+
+
+def test_models_items_restricted_restrict_rejects_roots():
+    """A root folder cannot be restricted."""
+    user = factories.UserFactory()
+    folder = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+
+    with pytest.raises(ValidationError, match="A root folder cannot be restricted"):
+        folder.restrict(user)
+
+
+def test_models_items_restricted_restrict_rejects_deleted():
+    """A deleted folder cannot be restricted."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    folder = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FOLDER)
+    parent.soft_delete()
+    folder.refresh_from_db()
+
+    with pytest.raises(ValidationError, match="A deleted folder cannot be restricted"):
+        folder.restrict(user)
+
+
+def test_models_items_restricted_cuts_role_inheritance():
+    """Roles inherited from former ancestors stop applying once restricted."""
+    parent_user = factories.UserFactory()
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(
+        type=models.ItemTypeChoices.FOLDER,
+        users=[(parent_user, models.RoleChoices.OWNER)],
+    )
+    folder = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FOLDER)
+
+    folder = folder.restrict(user)
+
+    assert folder.get_role(parent_user) is None
+    assert folder.get_role(user) == models.RoleChoices.OWNER
+
+
+def test_models_items_restricted_descendants_inherit_from_restricted_folder():
+    """Descendants inherit the explicit accesses of the restricted folder only."""
+    parent_user = factories.UserFactory()
+    user = factories.UserFactory()
+    reader = factories.UserFactory()
+    parent = factories.ItemFactory(
+        type=models.ItemTypeChoices.FOLDER,
+        users=[(parent_user, models.RoleChoices.OWNER)],
+    )
+    folder = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FOLDER)
+    child = factories.ItemFactory(parent=folder, type=models.ItemTypeChoices.FILE)
+    factories.UserItemAccessFactory(item=folder, user=reader, role="reader")
+
+    folder.restrict(user)
+
+    child.refresh_from_db()
+    assert child.get_role(reader) == models.RoleChoices.READER
+    assert child.get_role(parent_user) is None
+
+
+def test_models_items_restricted_cuts_link_inheritance():
+    """The link definition of former ancestors stops applying once restricted."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(
+        type=models.ItemTypeChoices.FOLDER,
+        link_reach=LinkReachChoices.PUBLIC,
+        link_role="editor",
+    )
+    folder = factories.ItemFactory(
+        parent=parent,
+        type=models.ItemTypeChoices.FOLDER,
+        link_reach=None,
+    )
+    child = factories.ItemFactory(parent=folder, type=models.ItemTypeChoices.FILE)
+
+    folder = folder.restrict(user)
+
+    child.refresh_from_db()
+    assert folder.computed_link_definition == {
+        "link_reach": LinkReachChoices.RESTRICTED,
+        "link_role": None,
+    }
+    assert child.computed_link_definition == {
+        "link_reach": LinkReachChoices.RESTRICTED,
+        "link_role": None,
+    }
+
+
+def test_models_items_restricted_move_rejects_restricted_roots():
+    """A restricted folder cannot be moved: it must be deactivated first."""
+    user = factories.UserFactory()
+    parent = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    folder = factories.ItemFactory(parent=parent, type=models.ItemTypeChoices.FOLDER)
+    other = factories.ItemFactory(type=models.ItemTypeChoices.FOLDER)
+    folder = folder.restrict(user)
+
+    with pytest.raises(ValidationError, match="A restricted folder cannot be moved"):
+        folder.move(other)

src/backend/core/tests/test_models_items_shortcuts.py

@@ -51,6 +51,18 @@ def test_models_items_shortcuts_deleted_with_their_target():
     assert not models.Item.objects.filter(pk=shortcut.pk).exists()
 
 
+def test_models_items_shortcuts_move_rejects_own_target_subtree():
+    """A shortcut cannot be moved under the subtree of its own target."""
+    shortcut = factories.ShortcutFactory()
+    folder = factories.ItemFactory(
+        parent=shortcut.target,
+        type=models.ItemTypeChoices.FOLDER,
+    )
+
+    with pytest.raises(ValidationError, match="cannot be moved under its own target"):
+        shortcut.move(folder)
+
+
 def test_models_items_shortcuts_item_factory_never_generates_shortcuts():
     """The generic item factory should only draw folder and file types."""
     types = {factories.ItemFactory().type for _ in range(20)}