refactor(cli): 提取 _build_upstream_request 统一流式/非流式的上游请求构建逻辑

将 cli_stream_mixin 和 cli_sync_mixin 中重复的上游请求构建代码
(provider behavior / stream policy / envelope / auth / RequestBuilder / URL 构建)
提取到 cli_request_mixin._build_upstream_request，返回 CliUpstreamRequestResult dataclass。

tests/api/handlers/base/test_cli_request_body_isolation.py

@@ -6,7 +6,8 @@ from typing import Any
 
 import pytest
 
-import src.api.handlers.base.cli_stream_mixin as mixmod
+import src.api.handlers.base.cli_request_mixin as request_mixmod
+from src.api.handlers.base.cli_request_mixin import CliRequestMixin
 from src.api.handlers.base.cli_stream_mixin import CliStreamMixin
 from src.api.handlers.base.stream_context import StreamContext
 
@@ -33,7 +34,7 @@ class _CaptureBuilder:
         raise _StopBuild()
 
 
-class _DummyCliStreamHandler(CliStreamMixin):
+class _DummyCliStreamHandler(CliRequestMixin, CliStreamMixin):
     FORMAT_ID = "openai:cli"
 
     def __init__(self) -> None:
@@ -79,9 +80,9 @@ async def test_execute_stream_request_does_not_mutate_original_request_body(
     async def _fake_get_provider_auth(endpoint: Any, key: Any) -> _DummyAuthInfo:
         return _DummyAuthInfo()
 
-    monkeypatch.setattr(mixmod, "get_provider_auth", _fake_get_provider_auth)
+    monkeypatch.setattr(request_mixmod, "get_provider_auth", _fake_get_provider_auth)
     monkeypatch.setattr(
-        mixmod,
+        request_mixmod,
         "get_provider_behavior",
         lambda **kwargs: SimpleNamespace(
             envelope=None,
@@ -89,15 +90,19 @@ async def test_execute_stream_request_does_not_mutate_original_request_body(
             cross_format_variant=None,
         ),
     )
-    monkeypatch.setattr(mixmod, "get_upstream_stream_policy", lambda *args, **kwargs: None)
+    monkeypatch.setattr(request_mixmod, "get_upstream_stream_policy", lambda *args, **kwargs: None)
     monkeypatch.setattr(
-        mixmod,
+        request_mixmod,
         "resolve_upstream_is_stream",
         lambda *, client_is_stream, policy: client_is_stream,
     )
-    monkeypatch.setattr(mixmod, "enforce_stream_mode_for_upstream", lambda *args, **kwargs: None)
     monkeypatch.setattr(
-        mixmod,
+        request_mixmod,
+        "enforce_stream_mode_for_upstream",
+        lambda *args, **kwargs: None,
+    )
+    monkeypatch.setattr(
+        request_mixmod,
         "maybe_patch_request_with_prompt_cache_key",
         lambda request_body, **kwargs: request_body,
     )
@@ -107,7 +112,12 @@ async def test_execute_stream_request_does_not_mutate_original_request_body(
     ctx.client_api_format = "openai:cli"
 
     provider = SimpleNamespace(name="provider", id="provider-1", provider_type="", proxy=None)
-    endpoint = SimpleNamespace(id="endpoint-1", api_format="openai:cli", base_url="https://x")
+    endpoint = SimpleNamespace(
+        id="endpoint-1",
+        api_format="openai:cli",
+        base_url="https://x",
+        custom_path=None,
+    )
     key = SimpleNamespace(id="key-1", proxy=None)
     candidate = SimpleNamespace(
         mapping_matched_model=None, needs_conversion=False, output_limit=None