fix(sandbox): patch Popen + block startfile to prevent window leaks

subprocess.run was already patched with CREATE_NO_WINDOW, but Popen and
os.startfile were unprotected. Agent code could open visible GUI windows
via subprocess.Popen(['notepad.exe']) or os.startfile().

assets/code_run_header.py

@@ -19,4 +19,12 @@ def _run(*a, **k):
         if r.stderr is not None: r.stderr = _d(r.stderr)
     return r
 subprocess.run = _run
+_Pi = subprocess.Popen.__init__
+def _pinit(self, *a, **k):
+    if os.name == 'nt': k['creationflags'] = (k.get('creationflags') or 0) | 0x08000000
+    _Pi(self, *a, **k)
+subprocess.Popen.__init__ = _pinit
+if hasattr(os, 'startfile'):
+    def _nosf(*a, **k): raise RuntimeError("startfile disabled in sandbox")
+    os.startfile = _nosf
 sys.excepthook = lambda t, v, tb: (sys.__excepthook__(t, v, tb), print(f"\n[Agent Hint]: NO GUESSING! You MUST probe first. If missing common package, pip.")) if issubclass(t, (ImportError, AttributeError)) else sys.__excepthook__(t, v, tb)