feat: Antigravity 和 Codex 服务支持

- 新增 Antigravity 服务：签名缓存、URL 可用性检测、信封处理
- 新增 Codex 服务：信封处理、元数据收集器
- 重构 provider transport 支持新的服务架构
- 新增 stream_bridge 和 upstream_stream_bridge 处理流式响应
- 优化 OAuth 工具函数
- 添加相关测试用例

tests/services/test_upstream_stream_policy.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from types import SimpleNamespace
+
+from src.services.provider.stream_policy import (
+    UpstreamStreamPolicy,
+    enforce_stream_mode_for_upstream,
+    get_upstream_stream_policy,
+)
+
+
+@dataclass
+class _DummyEndpoint:
+    api_format: str
+    config: dict | None = None
+    provider: object | None = None
+
+
+def test_get_upstream_stream_policy_defaults_to_auto() -> None:
+    ep = _DummyEndpoint(api_format="openai:chat", config=None, provider=SimpleNamespace(provider_type="custom"))
+    assert get_upstream_stream_policy(ep) == UpstreamStreamPolicy.AUTO
+
+
+def test_get_upstream_stream_policy_codex_openai_cli_forces_stream() -> None:
+    ep = _DummyEndpoint(
+        api_format="openai:cli",
+        config=None,
+        provider=SimpleNamespace(provider_type="codex"),
+    )
+    assert get_upstream_stream_policy(ep) == UpstreamStreamPolicy.FORCE_STREAM
+
+
+def test_get_upstream_stream_policy_codex_ignores_force_non_stream_config() -> None:
+    ep = _DummyEndpoint(
+        api_format="openai:cli",
+        config={"upstream_stream_policy": "force_non_stream"},
+        provider=SimpleNamespace(provider_type="codex"),
+    )
+    assert get_upstream_stream_policy(ep) == UpstreamStreamPolicy.FORCE_STREAM
+
+
+def test_enforce_stream_mode_for_upstream_openai_chat_sets_stream_options_usage() -> None:
+    body = {"stream": False}
+    out = enforce_stream_mode_for_upstream(
+        body,
+        provider_api_format="openai:chat",
+        upstream_is_stream=True,
+    )
+    assert out["stream"] is True
+    assert out["stream_options"]["include_usage"] is True
+
+
+def test_enforce_stream_mode_for_upstream_gemini_drops_stream_field() -> None:
+    body = {"stream": True, "foo": "bar"}
+    out = enforce_stream_mode_for_upstream(
+        body,
+        provider_api_format="gemini:chat",
+        upstream_is_stream=False,
+    )
+    assert "stream" not in out
+    assert out["foo"] == "bar"
+