feat: 添加 mycodex 入口，支持 OpenAI Codex CLI

- 在 launcher 中注册 codex 后端，兼容 ~/.codex/sessions 日期嵌套目录

- 解析 session_meta.payload.cwd 过滤当前目录会话

- 添加 myagents codex 子命令与 mycodex 独立入口、补全及 Makefile 链接

- 更新 pyproject.toml 控制台脚本与 README 文档

- 补充 codex 相关单元测试，45 tests passed

tests/test_entrypoints.py

@@ -1,11 +1,11 @@
-"""Tests for standalone myclaude / mykimi entrypoints."""
+"""Tests for standalone myclaude / mykimi / mycodex entrypoints."""
 
 from pathlib import Path
 from unittest.mock import MagicMock, patch
 
 from click.testing import CliRunner
 
-from myagents.entrypoints import claude_cli, kimi_cli
+from myagents.entrypoints import claude_cli, codex_cli, kimi_cli
 
 
 class TestMyclaudeEntrypoint:
@@ -73,3 +73,36 @@ class TestMykimiEntrypoint:
             result = runner.invoke(kimi_cli, ["--cwd", str(tmp_path), "--resume"])
             assert result.exit_code == 0
             assert "--resume" in mock_run.call_args[0][0]
+
+
+class TestMycodexEntrypoint:
+    """``mycodex`` standalone entrypoint."""
+
+    def test_runs_codex(self) -> None:
+        runner = CliRunner()
+        with (
+            patch("myagents.launcher.shutil.which", return_value="/usr/bin/codex"),
+            patch("myagents.launcher.subprocess.run") as mock_run,
+        ):
+            mock_run.return_value = MagicMock(returncode=0)
+            result = runner.invoke(codex_cli, [])
+            assert result.exit_code == 0
+            assert mock_run.call_args[0][0] == ["/usr/bin/codex"]
+
+    def test_version_shows_mycodex(self) -> None:
+        runner = CliRunner()
+        result = runner.invoke(codex_cli, ["--version"])
+        assert result.exit_code == 0
+        assert "mycodex" in result.output
+
+    def test_passthrough(self, tmp_path: Path) -> None:
+        runner = CliRunner()
+        with (
+            patch("myagents.launcher.shutil.which", return_value="/usr/bin/codex"),
+            patch("myagents.launcher.subprocess.run") as mock_run,
+        ):
+            mock_run.return_value = MagicMock(returncode=0)
+            result = runner.invoke(codex_cli, ["--cwd", str(tmp_path), "resume", "abc123"])
+            assert result.exit_code == 0
+            assert "resume" in mock_run.call_args[0][0]
+            assert "abc123" in mock_run.call_args[0][0]