fix(chat): strip thinking content from model output

Handle thinking models that return wrapped content even when
Thinking=false is configured. This is a fallback strategy for models
like MiniMax-M2.1 that do not fully support the Thinking parameter.
The thinking tags and their enclosed content are completely stripped.

internal/models/chat/remote_api.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"strings"
 
 	"github.com/Tencent/WeKnora/internal/logger"
 	"github.com/Tencent/WeKnora/internal/models/provider"
@@ -241,8 +242,13 @@ func (c *RemoteAPIChat) parseCompletionResponse(resp *openai.ChatCompletionRespo
 	}
 
 	choice := resp.Choices[0]
+
+	// 处理思考模型的输出：移除 <think></think> 标签包裹的思考过程
+	// 为设置了 Thinking=false 但模型仍返回思考内容的情况和部分不支持Thinking=false的思考模型(例如Miniax-M2.1)提供兜底策略
+	content := removeThinkingContent(choice.Message.Content)
+
 	response := &types.ChatResponse{
-		Content:      choice.Message.Content,
+		Content:      content,
 		FinishReason: string(choice.FinishReason),
 		Usage: struct {
 			PromptTokens     int `json:"prompt_tokens"`
@@ -272,6 +278,28 @@ func (c *RemoteAPIChat) parseCompletionResponse(resp *openai.ChatCompletionRespo
 	return response, nil
 }
 
+// removeThinkingContent 移除思考模型输出中的 <think></think> 思考过程
+// 仅当内容以 <think> 开头时才处理
+func removeThinkingContent(content string) string {
+	const thinkStartTag = "<think>"
+	const thinkEndTag = "</think>"
+
+	trimmed := strings.TrimSpace(content)
+	if !strings.HasPrefix(trimmed, thinkStartTag) {
+		return content
+	}
+
+	// 查找最后一个 </think> 标签（处理嵌套情况）
+	if lastEndIdx := strings.LastIndex(trimmed, thinkEndTag); lastEndIdx != -1 {
+		if result := strings.TrimSpace(trimmed[lastEndIdx+len(thinkEndTag):]); result != "" {
+			return result
+		}
+		return ""
+	}
+
+	return "" // 未找到 </think>，可能思考内容过长被截断，返回空字符串
+}
+
 // ChatStream 进行流式聊天
 func (c *RemoteAPIChat) ChatStream(ctx context.Context, messages []Message, opts *ChatOptions) (<-chan types.StreamResponse, error) {
 	req := c.BuildChatCompletionRequest(messages, opts, true)