The AI assistant is set to deepseek-v4-pro or deepseek-v4-flash, but cannot output the corresponding response.

The AI assistant is set to deepseek-v4-pro or deepseek-v4-flash, but cannot output the corresponding response.Output the error message: 'Error: Failed to create AI stream'

But when I set the AI assistant to deepseek-chat, it can output content, but it can only search for the question and cannot effectively retrieve the corresponding answer.

使用 deepseek-v4-pro 和 deepseek-v4-flash 复现该故障，然后在观察报告的“Failed to create AI stream”错误的同时，将其与 deepseek-chat 进行比较。跟踪 AI assistant 的流创建入口点和 provider 处理逻辑；当列出的两个模型都能在不出现该错误的情况下生成响应，并且已理解报告的检索行为时，即表示完成。

由索引模型根据 Issue 内容生成。