Add user_id Data Isolation for Reasonix System

[zeroro88]

Overview

Reasonix currently shares all user sessions, memory, task and API request resources globally without user_id isolation. When serving multiple end-users under one DeepSeek account, it will cause cross-user KV cache interference, scheduling conflicts and inaccurate rate limiting. We need to support configurable user_id to implement DeepSeek official multi-user isolation capabilities.

Why We Need This

• DeepSeek API supports user_id isolation, including KV Cache isolation, scheduling isolation and content safety isolation
• Without user_id isolation, different end-users’ reasoning contexts may conflict or leak with each other
• Lack of user-level independent concurrency rate limit, causing 429 inaccurate triggering in multi-user scenarios

Expected Features

• Configurable user_id (core)
• Support configuring static/dynamic user_id via Reasonix local config, no hardcode
  https://api-docs.deepseek.com/quick_start/rate_limit