OCR 500: GPU 回退 CPU、返回详细错误、增加 test-ocr 诊断。

backend/app/routers/wrong_questions.py

@@ -177,7 +177,8 @@ def _process_wrong_question(question_id: uuid.UUID):
             if "libGL" in str(exc):
                 msg += " 请在服务器执行: sudo bash deploy/install-ocr-deps.sh && systemctl restart grade-archive"
             elif ocr_url:
-                msg += f" 请检查 OCR 服务是否可达: {ocr_url} （可浏览器访问 {ocr_url.rstrip('/')}/health）"
+                if "OCR 服务" not in msg:
+                    msg += " 诊断: bash deploy/ocr-screen.sh status && bash deploy/ocr-worker/test-ocr.sh"
             wq.error_message = msg
             db.commit()
             return

backend/app/services/ocr.py

@@ -130,7 +130,17 @@ def _run_remote_ocr(service_url: str, image_path: str) -> dict:
         files = {"file": (Path(image_path).name, handle, "image/jpeg")}
         with httpx.Client(timeout=settings.OCR_TIMEOUT_SECONDS) as client:
             resp = client.post(url, files=files, headers=headers)
-            resp.raise_for_status()
+            if resp.status_code >= 400:
+                detail = resp.text
+                try:
+                    body = resp.json()
+                    if isinstance(body.get("detail"), str):
+                        detail = body["detail"]
+                    elif isinstance(body.get("detail"), list):
+                        detail = str(body["detail"])
+                except Exception:
+                    pass
+                raise RuntimeError(f"OCR 服务 {resp.status_code}: {detail}")
             return resp.json()