fix: AI 流式回复过滤思考标签 + 加载历史上下文

- ChatAgentService.RunStreamingAsync 增加状态机过滤 qwen3 <think/> 标签
- RunAsync 同步方法也增加过滤
- StreamMessageEndpoint 从 Redis/DB 加载历史消息构建上下文

src/RAG.Api/Endpoints/Chat/StreamMessageEndpoint.cs

@@ -1,6 +1,7 @@
 using System.Text;
 using System.Text.Json;
 using FastEndpoints;
+using Microsoft.EntityFrameworkCore;
 using RAG.Domain.Entities;
 using RAG.Domain.Enums;
 using RAG.Domain.Interfaces;
@@ -40,6 +41,43 @@ public class StreamMessageEndpoint(RagDbContext db, IAIChatAgent chatAgent, ICha
         await cache.AppendMessageAsync(conversationId,
             new CachedChatMessage(userMessage.Id, ChatRole.User.ToString(), userMessage.Content, null, userMessage.CreatedAt), ct);
 
+        // 加载历史消息构建上下文
+        var cached = await cache.GetMessagesAsync(conversationId, ct);
+        List<(string Role, string Content)> history;
+        if (cached is { Count: > 0 })
+        {
+            history = cached
+                .OrderBy(m => m.CreatedAt)
+                .Select(m => (m.Role, m.Content))
+                .ToList();
+        }
+        else
+        {
+            var dbMessages = await db.ChatMessages
+                .Where(m => m.ConversationId == conversationId)
+                .OrderBy(m => m.CreatedAt)
+                .ToListAsync(ct);
+
+            history = dbMessages.Select(m => (m.Role.ToString(), m.Content)).ToList();
+
+            // 回填 Redis 缓存
+            if (history.Count > 0)
+            {
+                await cache.SetMessagesAsync(conversationId,
+                    history.Select((h, i) => new CachedChatMessage(
+                        Guid.NewGuid(), h.Item1, h.Item2, null,
+                        DateTime.UtcNow.AddSeconds(i))).ToList(), ct);
+            }
+        }
+
+        var promptBuilder = new StringBuilder();
+        foreach (var (role, content) in history)
+        {
+            promptBuilder.AppendLine($"{role}: {content}");
+        }
+
+        var prompt = promptBuilder.ToString();
+
         // SSE 响应
         HttpContext.Response.ContentType = "text/event-stream";
         HttpContext.Response.Headers.CacheControl = "no-cache";
@@ -47,7 +85,7 @@ public class StreamMessageEndpoint(RagDbContext db, IAIChatAgent chatAgent, ICha
 
         var fullReply = new StringBuilder();
 
-        await foreach (var chunk in chatAgent.RunStreamingAsync(req.Content, ct))
+        await foreach (var chunk in chatAgent.RunStreamingAsync(prompt, ct))
         {
             fullReply.Append(chunk);
             var sseData = JsonSerializer.Serialize(new { content = chunk });
@@ -69,7 +107,7 @@ public class StreamMessageEndpoint(RagDbContext db, IAIChatAgent chatAgent, ICha
         await cache.AppendMessageAsync(conversationId,
             new CachedChatMessage(assistantMessage.Id, ChatRole.Assistant.ToString(), assistantMessage.Content, null, assistantMessage.CreatedAt), ct);
 
-        // 发送结束标记（含完整消息 ID）
+        // 发送结束标记
         var doneData = JsonSerializer.Serialize(new { messageId = assistantMessage.Id });
         await HttpContext.Response.WriteAsync($"event: done\ndata: {doneData}\n\n", ct);
         await HttpContext.Response.Body.FlushAsync(ct);

src/RAG.Infrastructure/AI/ChatAgentService.cs

@@ -1,4 +1,5 @@
 using System.Runtime.CompilerServices;
+using System.Text;
 using System.ClientModel;
 using Microsoft.Agents.AI;
 using Microsoft.Extensions.Options;
@@ -28,16 +29,142 @@ public class ChatAgentService : IAIChatAgent
     public async Task<string> RunAsync(string prompt, CancellationToken ct)
     {
         var response = await _agent.RunAsync(prompt, null, null, ct);
-        return response.Text;
+        return FilterThinkTags(response.Text);
     }
 
     public async IAsyncEnumerable<string> RunStreamingAsync(
         string prompt, [EnumeratorCancellation] CancellationToken ct)
     {
+        // 状态机过滤 <think...>...</think\> 标签
+        var buffer = new StringBuilder();
+        var inThink = false;
+
         await foreach (var update in _agent.RunStreamingAsync(prompt, null, null, ct))
         {
-            if (!string.IsNullOrEmpty(update.Text))
+            if (string.IsNullOrEmpty(update.Text))
-                yield return update.Text;
+                continue;
+
+            buffer.Append(update.Text);
+
+            // 从 buffer 中提取可以安全输出的文本
+            while (buffer.Length > 0)
+            {
+                var content = buffer.ToString();
+
+                if (inThink)
+                {
+                    var endIdx = content.IndexOf("</think", StringComparison.Ordinal);
+                    if (endIdx < 0)
+                    {
+                        // 还在 think 块内，保留尾部以防截断
+                        if (buffer.Length > 10)
+                            buffer.Remove(0, buffer.Length - 10);
+                        break;
+                    }
+
+                    // 找到结束标签，跳过 </think\>
+                    var closeIdx = content.IndexOf('>', endIdx);
+                    if (closeIdx < 0)
+                        break;
+
+                    inThink = false;
+                    buffer.Remove(0, closeIdx + 1);
+                }
+                else
+                {
+                    var thinkIdx = content.IndexOf("<think", StringComparison.Ordinal);
+                    if (thinkIdx < 0)
+                    {
+                        // 没有 think 标签，全部输出（保留尾部 7 字符防截断）
+                        if (buffer.Length > 7)
+                        {
+                            var safeLen = buffer.Length - 7;
+                            var output = buffer.ToString(0, safeLen);
+                            buffer.Remove(0, safeLen);
+                            if (output.Length > 0)
+                                yield return output;
+                        }
+
+                        break;
+                    }
+
+                    // 输出 think 标签之前的内容
+                    if (thinkIdx > 0)
+                        yield return buffer.ToString(0, thinkIdx);
+
+                    // 检查同一 chunk 内是否有 </think\>
+                    var endIdx = content.IndexOf("</think", thinkIdx, StringComparison.Ordinal);
+                    if (endIdx >= 0)
+                    {
+                        var closeIdx = content.IndexOf('>', endIdx);
+                        if (closeIdx >= 0)
+                        {
+                            // 完整的 think 块在同一 chunk，直接跳过
+                            buffer.Remove(0, closeIdx + 1);
+                        }
+                        else
+                        {
+                            // 有结束标签但不完整
+                            inThink = true;
+                            buffer.Clear();
+                            break;
+                        }
+                    }
+                    else
+                    {
+                        // 进入 think 块
+                        inThink = true;
+                        buffer.Remove(0, thinkIdx);
+                        break;
+                    }
+                }
+            }
         }
+
+        // 输出 buffer 中剩余的非 think 内容
+        if (!inThink && buffer.Length > 0)
+            yield return buffer.ToString();
+
+        buffer.Clear();
+    }
+
+    /// <summary>过滤完整的文本中的 think 标签（非流式用）</summary>
+    private static string FilterThinkTags(string text)
+    {
+        if (string.IsNullOrEmpty(text)) return text;
+
+        var sb = new StringBuilder();
+        var span = text.AsSpan();
+        while (!span.IsEmpty)
+        {
+            var thinkStart = span.IndexOf("<think".AsSpan());
+            if (thinkStart < 0)
+            {
+                sb.Append(span);
+                break;
+            }
+
+            // 添加 think 标签之前的内容
+            sb.Append(span[..thinkStart]);
+
+            // 找到 </think\>
+            var afterThink = span[(thinkStart + 6)..];
+            var gtIdx = afterThink.IndexOf('>');
+            if (gtIdx < 0)
+                break;
+
+            var endTag = afterThink[(gtIdx + 1)..].IndexOf("</think".AsSpan());
+            if (endTag < 0)
+                break;
+
+            var afterEnd = afterThink[(gtIdx + 1 + endTag)..];
+            var endGt = afterEnd.IndexOf('>');
+            if (endGt < 0)
+                break;
+
+            span = afterEnd[(endGt + 1)..];
+        }
+
+        return sb.ToString().TrimStart('\n', '\r');
     }
 }