feat: preserve governed OpenAI tool messages in 1.4.0

Add faithful single-choice chat results, tool stream activity, error-frame retries, and isolated protocol caching.

Reject empty cached completions with the same value predicate as transport, add regression coverage, and adopt Apache-2.0.

tests/unit/test_package.py

@@ -88,3 +88,15 @@ def test_every_promised_export_is_actually_importable():
     """
     missing = [name for name in polygateway.__all__ if not hasattr(polygateway, name)]
     assert not missing, f"__all__ 承诺了但没绑上的符号: {missing}"
+
+
+def test_apache_license_metadata():
+    """许可正文和包元数据同时存在，不以版本说明替代许可。"""
+    import tomllib
+    from pathlib import Path
+
+    root = Path(__file__).resolve().parents[2]
+    assert "Apache License" in (root / "LICENSE").read_text()
+    assert "Version 2.0" in (root / "LICENSE").read_text()
+    project = tomllib.loads((root / "pyproject.toml").read_text())["project"]
+    assert project["license"] == {"file": "LICENSE"}