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_request_builder_oauth.py

@@ -0,0 +1,46 @@
+from __future__ import annotations
+
+import json
+import time
+from types import SimpleNamespace
+from unittest.mock import patch
+
+import pytest
+
+from src.api.handlers.base.request_builder import get_provider_auth
+
+
+@pytest.mark.asyncio
+async def test_get_provider_auth_oauth_returns_decrypted_auth_config() -> None:
+    now = int(time.time())
+    token_meta = {
+        "provider_type": "antigravity",
+        "expires_at": now + 3600,
+        "refresh_token": "rt-1",
+        "project_id": "project-1",
+    }
+
+    endpoint = SimpleNamespace(api_format="gemini:cli")
+    key = SimpleNamespace(
+        id="k1",
+        auth_type="oauth",
+        api_key="enc_access",
+        auth_config="enc_cfg",
+        provider=None,
+    )
+
+    def _decrypt(v):  # noqa: ANN001
+        if v == "enc_access":
+            return "access-token"
+        if v == "enc_cfg":
+            return json.dumps(token_meta)
+        return ""
+
+    with patch("src.api.handlers.base.request_builder.crypto_service.decrypt", side_effect=_decrypt):
+        auth = await get_provider_auth(endpoint, key)  # type: ignore[arg-type]
+
+    assert auth is not None
+    assert auth.auth_header == "Authorization"
+    assert auth.auth_value == "Bearer access-token"
+    assert auth.decrypted_auth_config == token_meta
+