Stub binary doesn't support `sys.executable` spawn/multiprocessing

**Describe the bug**
When multiprocessing is used to fork a subprocess, the main program entrypoint is executed in the subprocess rather than the Process target.

**To Reproduce**
create a `multiprocessing.Process()` and start it using `.start()` The subprocess will call the parent process entry point.

**Expected behavior**
The target function is called as the entrypoint of the subprocess

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Environment:**
- Operating System: macOS
- Python version: 3.10

**Additional context**
Add any other context about the problem here.

Start by reproducing the macOS behavior with multiprocessing.Process().start() and inspect how the template's stub binary handles sys.executable and subprocess startup. Confirm that the child invokes the Process target rather than the parent entry point, then add or update a regression test if the repository provides one.

Written by the indexing model from the issue text.