Support DeepSeek V4 Thinking Mode with reasoning_content handling #24114

Description

According to DeepSeek's official documentation (https://api-docs.deepseek.com/guides/thinking_mode), when thinking mode is enabled:

1. The API returns both reasoning_content (thinking process) and content (final answer)
2. In multi-turn conversations with tool calls, the reasoning_content must be passed back to the API in subsequent requests
3. If reasoning_content is not properly preserved and returned, the API returns a 400 error
   Currently, OpenCode's AI SDK does not preserve or pass back the reasoning_content field in multi-turn conversations, causing this error.
   Expected Behavior
   OpenCode should:
4. Capture reasoning_content from DeepSeek API responses
5. Store it alongside the regular content in conversation history
6. Pass it back in subsequent API calls when continuing the conversation
   Current Workaround
   Users must explicitly disable thinking mode in their configuration:
   { "provider": { "deepseekv4": { "npm": "@ai-sdk/openai-compatible", "options": { "baseURL": "https://api.deepseek.com", "apiKey": "sk-xxx" }, "models": { "deepseek-v4-pro": { "name": "deepseek-v4-pro", "extra_body": { "thinking": { "type": "disabled" } } } } } } }
   This works but disables the powerful thinking capabilities of DeepSeek V4.
   Proposed Solution
   Modify the message handling logic to:
7. Check if the response contains a reasoning_content field
8. Store it in the message object alongside content
9. When constructing the next request, include reasoning_content for assistant messages that had it
   Example implementation (pseudo-code):
   // When receiving response
   const assistantMessage = {
   role: 'assistant',
   content: response.choices[0].message.content,
   reasoning_content: response.choices[0].message.reasoning_content, // Preserve this
   tool_calls: response.choices[0].message.tool_calls
   }
   // When sending next request
   messages.push(assistantMessage) // Include reasoning_content if present
   Reference Documentation

• DeepSeek Thinking Mode Guide (https://api-docs.deepseek.com/guides/thinking_mode)
• Multi-round Chat with Thinking Mode (https://api-docs.deepseek.com/guides/thinking_mode#multi-round-conversation)
• Tool Calls with Thinking Mode (https://api-docs.deepseek.com/guides/thinking_mode#tool-calls)
  Environment
• OpenCode Version: 1.14.22
• Platform: Windows x64
• Model: DeepSeek V4 Pro/Flash
• Provider: @ai-sdk/openai-compatible
  Additional Context
  DeepSeek V4's thinking mode significantly improves reasoning quality for complex tasks. Supporting this feature would make OpenCode more competitive with other AI coding assistants that already support DeepSeek's full capabilities.

Plugins

No response

OpenCode version

No response

Steps to reproduce

No response

Screenshot and/or share link

No response

Operating System

No response

Terminal

No response