fix: use windows sandbox fallback for harness

scripts/execute.py

@@ -251,9 +251,10 @@ class StepExecutor:
             sys.exit(1)
 
         prompt = preamble + step_file.read_text(encoding="utf-8")
-        command = [
+        command = ["codex", "exec"]
-            "codex",
+        if os.name == "nt":
-            "exec",
+            command.extend(["-c", 'windows.sandbox="unelevated"'])
+        command.extend([
             "--json",
             "--sandbox",
             "workspace-write",
@@ -261,7 +262,7 @@ class StepExecutor:
             "--cd",
             self._root,
             "-",
-        ]
+        ])
         try:
             result = subprocess.run(
                 command,

tests/test_execute.py

@@ -34,6 +34,9 @@ def test_invoke_codex_uses_utf8_for_unicode_prompt(tmp_path, monkeypatch):
 
     assert "Euler–Bernoulli 보" in invocation["kwargs"]["input"]
     assert invocation["kwargs"]["encoding"] == "utf-8"
+    if execute.os.name == "nt":
+        config_index = invocation["command"].index("-c")
+        assert invocation["command"][config_index + 1] == 'windows.sandbox="unelevated"'
 
 
 def test_run_git_decodes_output_as_utf8(tmp_path, monkeypatch):