fix(windows): preserve registry separators during template expansion

scripts/render-per-user-wix.py

@@ -64,7 +64,7 @@ def registry_key(name: str) -> ET.Element:
         "RegistryValue",
         {
             "Root": "HKCU",
-            "Key": r"Software\{{@root.manufacturer}}\{{@root.product_name}}\Components",
+            "Key": r"Software\\{{@root.manufacturer}}\\{{@root.product_name}}\Components",
             "Name": name,
             "Type": "integer",
             "Value": "1",

tests/test_windows_per_user_installer.py

@@ -166,3 +166,10 @@ def test_external_binary_guid_is_explicit_and_stable_across_builds():
     assert first_guid == second.split(marker)[1].split(" Win64=")[0]
     assert '(eq bin.id "helper.exe")' in first_guid
     assert 'Guid="*"' not in marker + first_guid
+
+
+def test_registry_key_template_does_not_escape_handlebars_expressions():
+    key = _renderer().registry_key("MainBinary").attrib["Key"]
+    # A single backslash escapes the opening Handlebars delimiter. The canonical
+    # WiX template doubles it so the installed key uses resolved product names.
+    assert key == r"Software\\{{@root.manufacturer}}\\{{@root.product_name}}\Components"