fix: resolve codex shim for harness runner

scripts/execute.py

@@ -12,6 +12,7 @@ import fnmatch
 import json
 import os
 import re
+import shutil
 import subprocess
 import sys
 import threading
@@ -373,7 +374,7 @@ class StepExecutor:
 
         prompt = preamble + step_file.read_text(encoding="utf-8")
         result = subprocess.run(
-            ["codex", "exec", "--dangerously-bypass-approvals-and-sandbox", "--json", "-"],
+            [self._codex_command(), "exec", "--dangerously-bypass-approvals-and-sandbox", "--json", "-"],
             cwd=self._root, capture_output=True, text=True, input=prompt, timeout=1800,
         )
 
@@ -395,6 +396,15 @@ class StepExecutor:
 
     # --- 헤더 & 검증 ---
 
+    @staticmethod
+    def _codex_command() -> str:
+        return (
+            shutil.which("codex.cmd")
+            or shutil.which("codex.exe")
+            or shutil.which("codex")
+            or "codex"
+        )
+
     def _print_header(self):
         print(f"\n{'='*60}")
         print(f"  Harness Step Executor")