Maybe this?

Author: carmocca

setup.py

@@ -41,7 +41,6 @@
 """
 import contextlib
 import os
-import sys
 import tempfile
 from importlib.util import module_from_spec, spec_from_file_location
 from types import ModuleType
@@ -116,8 +115,8 @@ def _set_manifest_path(manifest_dir: str, aggregate: bool = False) -> Generator:
     setup_tools = _load_py_module(name="setup_tools", location=os.path.join(_PATH_ROOT, ".actions", "setup_tools.py"))
     assistant = _load_py_module(name="assistant", location=os.path.join(_PATH_ROOT, ".actions", "assistant.py"))
 
-    is_wheel_install = "sdist" not in sys.argv and "bdist_wheel" not in sys.argv and not os.path.exists(_PATH_SRC)
-    print("is_wheel_install:", is_wheel_install, sys.argv)
+    is_wheel_install = not os.path.exists(_PATH_SRC) or "PEP517_BUILD_BACKEND" in os.environ
+    print("is_wheel_install:", is_wheel_install)
 
     if not is_wheel_install:
         # copy the version information to all packages
@@ -136,7 +135,7 @@ def _set_manifest_path(manifest_dir: str, aggregate: bool = False) -> Generator:
     # if it's a wheel, iterate over all possible packages until we find one that can be installed.
     # the wheel should have included only the relevant files of the package to install
     possible_packages = (
-        _PACKAGE_MAPPING.values() if _PACKAGE_NAME is None or is_wheel_install else [_PACKAGE_MAPPING[_PACKAGE_NAME]]
+        _PACKAGE_MAPPING.values() if _PACKAGE_NAME is None and is_wheel_install else [_PACKAGE_MAPPING[_PACKAGE_NAME]]
     )
     for pkg in possible_packages:
         pkg_path = os.path.join(_PATH_SRC, pkg)