diff --git a/swe_af/runtime/codex_harness_patch.py b/swe_af/runtime/codex_harness_patch.py
index 96eaa3fb..79ddbf35 100644
--- a/swe_af/runtime/codex_harness_patch.py
+++ b/swe_af/runtime/codex_harness_patch.py
@@ -88,8 +88,16 @@ async def _run_codex_cli_with_stdin(
     env: dict[str, str] | None,
     cwd: str | None,
 ) -> tuple[str, str, int]:
+    # Windows: CreateProcess does no PATHEXT resolution, and npm installs the
+    # codex CLI only as a .cmd shim — spawning the bare name raises
+    # FileNotFoundError ([WinError 2]) on every call even though the shell
+    # finds it. resolve_cli_command resolves the shim's real path via
+    # shutil.which (a no-op on POSIX and for names that already carry a path).
+    from agentfield.harness._cli import resolve_cli_command
+
     proc = await asyncio.create_subprocess_exec(
-        *cmd,
+        resolve_cli_command(cmd[0]),
+        *cmd[1:],
         stdin=asyncio.subprocess.PIPE,
         stdout=asyncio.subprocess.PIPE,
         stderr=asyncio.subprocess.PIPE,
diff --git a/tests/test_codex_harness_patch.py b/tests/test_codex_harness_patch.py
index 3919e977..405b69e2 100644
--- a/tests/test_codex_harness_patch.py
+++ b/tests/test_codex_harness_patch.py
@@ -108,3 +108,46 @@ def test_non_codex_prompt_suffix_keeps_agentfield_write_tool_default(tmp_path) -
 
     assert "Write tool" in suffix
     assert "Codex CLI" not in suffix
+
+
+def test_run_codex_cli_spawns_via_resolved_command(monkeypatch) -> None:
+    """The spawn must route cmd[0] through the SDK's resolve_cli_command.
+
+    On Windows, npm installs the codex CLI only as a .cmd shim, and
+    CreateProcess does no PATHEXT resolution — spawning the bare name fails
+    with FileNotFoundError ([WinError 2]) on every codex harness call.
+    resolve_cli_command resolves the shim's real path (no-op on POSIX).
+    """
+    import asyncio
+
+    import agentfield.harness._cli as sdk_cli
+
+    from swe_af.runtime.codex_harness_patch import _run_codex_cli_with_stdin
+
+    spawned: dict = {}
+
+    class FakeProc:
+        returncode = 0
+
+        async def communicate(self, data: bytes) -> tuple[bytes, bytes]:
+            spawned["stdin"] = data
+            return b"", b""
+
+    async def fake_exec(program: str, *args: str, **kwargs: object) -> FakeProc:
+        spawned["program"] = program
+        spawned["args"] = args
+        return FakeProc()
+
+    monkeypatch.setattr(sdk_cli, "resolve_cli_command", lambda name: f"resolved::{name}")
+    monkeypatch.setattr(asyncio, "create_subprocess_exec", fake_exec)
+
+    stdout, stderr, returncode = asyncio.run(
+        _run_codex_cli_with_stdin(
+            ["codex", "exec", "--json"], "prompt", env=None, cwd=None
+        )
+    )
+
+    assert spawned["program"] == "resolved::codex"
+    assert spawned["args"][:2] == ("exec", "--json")
+    assert spawned["stdin"] == b"prompt"
+    assert (stdout, stderr, returncode) == ("", "", 0)