fix: decode harness git output as utf-8

tests/test_execute.py

@@ -34,3 +34,28 @@ 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"
+
+
+def test_run_git_decodes_output_as_utf8(tmp_path, monkeypatch):
+    invocation = {}
+
+    def capture_run(command, **kwargs):
+        invocation["command"] = command
+        invocation["kwargs"] = kwargs
+        return subprocess.CompletedProcess(command, 0, stdout="", stderr="")
+
+    monkeypatch.setattr(execute.subprocess, "run", capture_run)
+    executor = object.__new__(execute.StepExecutor)
+    executor._root = str(tmp_path)
+
+    executor._run_git("status", "--short")
+
+    assert invocation["kwargs"]["encoding"] == "utf-8"
+
+
+def test_feature_commit_message_is_windows_console_safe():
+    message = execute.StepExecutor.FEAT_MSG.format(
+        phase="linear-static-3d-euler-beam", num=0, name="requirements-baseline"
+    )
+
+    message.encode("cp949")