[BUG] DeepSeek 400 Error: The reasoning_content in the thinking mode must be passed back #209

Environment

• Date/time: 2026-05-20T04:17:59.609Z
• Extension version: 3.55.100066
• Provider: DeepSeek
• Model: deepseek-v4-flash

Bug Description

When using deepseek-v4-flash for multi-turn conversations, the API returns a 400 error.

Error Message

DeepSeek completion error: 400 The reasoning_content in the thinking mode must be passed back to the API.

Root Cause

DeepSeek's API requires that the reasoning_content from previous assistant responses must be included and passed back in the message history during subsequent requests. The extension currently filters out or misses this field, leading to API rejection.