Tree: Reorder... for a component's children

Right-click a component (or the app) with two or more children to move them
up and down; OK applies the new order, which is the order they run in. On a
device the order goes there first via Sox reorder, checked against the
device's children, and the file is left alone if it is refused. Undoable.

Also: device host in editor.properties.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

undo.py

@@ -378,3 +378,44 @@ class LiveRenameCommand(RenameComponentCommand):
             raise LiveUndoError(f"{self.old_name} was not renamed to {self.new_name} "
                                 "on the device")
         super().redo()
+
+
+def apply_child_order(parent, ordered_children):
+    """Puts `parent`'s <comp> children in the given order; its other children stay put."""
+    children = list(parent)
+    comp_slots = [i for i, child in enumerate(children) if child.tag == "comp"]
+    for slot, child in zip(comp_slots, ordered_children):
+        children[slot] = child
+    parent[:] = children
+
+
+class ReorderChildrenCommand:
+    """A new order for a component's children."""
+
+    def __init__(self, parent, old_order, new_order, label="reorder"):
+        self.parent = parent
+        self.old_order = list(old_order)
+        self.new_order = list(new_order)
+        self.label = label
+
+    def undo(self):
+        apply_child_order(self.parent, self.old_order)
+
+    def redo(self):
+        apply_child_order(self.parent, self.new_order)
+
+
+class LiveReorderChildrenCommand(ReorderChildrenCommand):
+    """A reorder on the device: the old order goes back there before the DOM takes it."""
+
+    def undo(self):
+        if not live_hooks.live_reorder_children(self.parent, self.old_order):
+            raise LiveUndoError(f"The old order of {self.parent.get('name', 'app')} "
+                                "could not be put back on the device")
+        super().undo()
+
+    def redo(self):
+        if not live_hooks.live_reorder_children(self.parent, self.new_order):
+            raise LiveUndoError(f"{self.parent.get('name', 'app')} was not reordered "
+                                "on the device")
+        super().redo()