fix: MCP插件TimeoutError修复 + 多项Bug修复和性能优化

- fix: MCP插件管理接口改为后台任务，修复TimeoutError
- fix: MCP连接失败后上下文清理的cancel scope错误
- feat: MCP插件后台注册添加重试机制
- fix: 限制每章自动创建伏笔数量上限
- fix: 修复JSON非法转义字符清洗
- fix: SSE流式生成添加心跳保活
- fix: 职业生成改用POST请求避免URL长度限制
- perf: 使用torch CPU版本加速Docker构建
- fix: 自动修复JSON字符串值中的裸换行符
- feat: 集成json5容错解析器

backend/app/api/characters.py

@@ -7,7 +7,7 @@ import json
 from typing import AsyncGenerator
 
 from app.database import get_db
-from app.utils.sse_response import SSEResponse, create_sse_response, WizardProgressTracker
+from app.utils.sse_response import SSEResponse, create_sse_response, WizardProgressTracker, wrap_stream_with_heartbeat, HEARTBEAT
 from app.models.character import Character
 from app.models.project import Project
 from app.models.generation_history import GenerationHistory
@@ -20,6 +20,7 @@ from app.schemas.character import (
     CharacterGenerateRequest
 )
 from app.services.ai_service import AIService
+from app.services.json_helper import loads_json
 from app.services.prompt_service import prompt_service, PromptService
 from app.services.import_export_service import ImportExportService
 from app.schemas.import_export import CharactersExportRequest, CharactersImportResult
@@ -947,10 +948,18 @@ async def generate_character_stream(
                 logger.info(f"🎯 开始生成角色（流式模式）...")
                 yield await tracker.generating(0, estimated_total, "开始生成角色...")
                 
-                async for chunk in user_ai_service.generate_text_stream(
-                    prompt=prompt,
-                    tool_choice="required",
+                async for chunk in wrap_stream_with_heartbeat(
+                    user_ai_service.generate_text_stream(
+                        prompt=prompt,
+                        tool_choice="required",
+                    ),
+                    heartbeat_interval=15.0
                 ):
+                    # 心跳哨兵：发送心跳保活，不混入AI响应
+                    if chunk is HEARTBEAT:
+                        yield await tracker.heartbeat()
+                        continue
+
                     # chunk 现在可能是 dict 或 str，提取 content 字段
                     if isinstance(chunk, dict):
                         content = chunk.get("content", "")
@@ -987,7 +996,7 @@ async def generate_character_stream(
             # ✅ 使用统一的 JSON 清洗方法
             try:
                 cleaned_response = user_ai_service._clean_json_response(ai_response)
-                character_data = json.loads(cleaned_response)
+                character_data = loads_json(cleaned_response)
                 logger.info(f"✅ 角色JSON解析成功")
             except json.JSONDecodeError as e:
                 logger.error(f"❌ 角色JSON解析失败: {e}")