refactor: centralize llm provider transport

app/backend/features/review/agent.py

@@ -1,12 +1,10 @@
 from __future__ import annotations
 
 import json
-import urllib.error
-import urllib.request
 from collections.abc import Iterator
 from typing import Any
 
-from llm_stream import OpenAIStreamAccumulator
+from backend.llm import transport as llm_transport
 
 
 class ReviewAssistantError(RuntimeError):
@@ -27,48 +25,20 @@ def stream_review_assistant(
     messages = [{"role": "system", "content": _system_prompt(context)}]
     messages.extend(history[-12:])
     messages.append({"role": "user", "content": question})
-    request = urllib.request.Request(
-        f"{base_url.rstrip('/')}/chat/completions",
-        data=json.dumps(
-            {"model": model, "messages": messages, "stream": True}, ensure_ascii=False
-        ).encode("utf-8"),
-        headers={
-            "Content-Type": "application/json",
-            "Authorization": f"Bearer {api_key}",
-            "User-Agent": "XiaobaiReviewWeb/1.0",
-            "Accept": "text/event-stream",
-        },
-        method="POST",
-    )
     try:
-        with urllib.request.urlopen(request, timeout=timeout) as response:
-            yielded = False
-            accumulator = OpenAIStreamAccumulator()
-            for raw_line in response:
-                line = raw_line.decode("utf-8", errors="replace").strip()
-                if not line or line.startswith(":"):
-                    continue
-                if line.startswith("data:"):
-                    line = line[5:].strip()
-                if line == "[DONE]":
-                    break
-                try:
-                    payload = json.loads(line)
-                except json.JSONDecodeError:
-                    continue
-                choices = payload.get("choices") or []
-                if not choices:
-                    continue
-                choice = choices[0] or {}
-                content = accumulator.feed(choice)
-                if content:
-                    yielded = True
-                    yield str(content)
-            if not yielded:
-                raise ReviewAssistantError("智能解读未返回有效内容。")
-    except urllib.error.HTTPError as exc:
+        yield from llm_transport.stream_chat_completion(
+            api_key=api_key,
+            base_url=base_url,
+            model=model,
+            messages=messages,
+            timeout=timeout,
+            user_agent="XiaobaiReviewWeb/1.0",
+        )
+    except llm_transport.OpenAIEmptyResponseError as exc:
+        raise ReviewAssistantError("智能解读未返回有效内容。") from exc
+    except llm_transport.OpenAIHTTPError as exc:
         raise ReviewAssistantError(f"智能解读服务暂不可用（{exc.code}）。") from exc
-    except (urllib.error.URLError, TimeoutError, OSError) as exc:
+    except llm_transport.OpenAITransportError as exc:
         raise ReviewAssistantError("智能解读连接中断，请稍后重试。") from exc