修复 AI 回复为空与开头数字被吞

日志里一批「成功但回复为空」的调用，completion tokens 恰好等于配置的
上限 256：推理模型把预算全花在思维链上，正文没写出来就被截断。

- 解析 OpenAI 兼容响应时读取 reasoning_content，并据此与 finish_reason
  判断「被截断」。
- 被截断时自动加大预算重试一次（4 倍，下限 1024、上限 4096），两次调用
  都记入日志以便核算成本；重试后仍为空才报错，并说明是推理占满预算，
  提示调高 tokens 或改用非推理模型。
- sanitizeAIReply 原本用 TrimLeft 去掉列表符号，连同任何开头的数字一起
  吃掉了——「30岁啦」发出去变成「岁啦」。改为只匹配真正的列表前缀
  （- * • 或 "1. " "2、"），号码、年龄、时长都不再受损。

线上两台已将模型 max_tokens 由 256 调整为 2048。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

im/backend/internal/app/ai_agent.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"log"
 	"math/rand"
+	"regexp"
 	"strings"
 	"sync"
 	"time"
@@ -258,14 +259,31 @@ func (a *App) processAIReplyJob(ctx context.Context, job aiReplyJob) error {
 	result, callErr := provider.Chat(callCtx, request)
 	latency := int(time.Since(started).Milliseconds())
 	a.logAICall(ctx, model.ID, "chat", job.AgentUserID, job.ConversationID, latency, result, callErr)
+	// Reasoning models spend the budget thinking before they answer. With a
+	// small ceiling the call "succeeds" with nothing to say, so give it room and
+	// ask once more rather than logging a silent empty reply.
+	if callErr == nil && result.truncated() {
+		retry := request
+		retry.MaxTokens = aiRetryMaxTokens(aiRequestMaxTokens(request, model))
+		retryCtx, cancelRetry := context.WithTimeout(ctx, time.Duration(model.TimeoutMS+2000)*time.Millisecond)
+		started = time.Now()
+		result, callErr = provider.Chat(retryCtx, retry)
+		cancelRetry()
+		a.logAICall(ctx, model.ID, "chat", job.AgentUserID, job.ConversationID, int(time.Since(started).Milliseconds()), result, callErr)
+	}
 	if callErr != nil {
 		if fallback := strings.TrimSpace(a.configPlain(ctx, "ai.fallback_text", "")); fallback != "" {
 			_ = a.sendAIReply(ctx, job, fallback)
 		}
 		return callErr
 	}
+	// A short answer that survived the retry is still worth sending; only an
+	// empty one is a failure.
 	text := sanitizeAIReply(result.Text)
 	if text == "" {
+		if result.truncated() {
+			return fmt.Errorf("模型把 %d tokens 全部用于推理，未产出正文；请在模型配置中调高最大 tokens，或改用非推理模型", result.CompletionTokens)
+		}
 		return fmt.Errorf("模型返回内容为空")
 	}
 	if first && a.configBool(ctx, "ai.disclose_in_chat", true) {
@@ -433,6 +451,11 @@ func aiSystemPrompt(binding aiAgentBinding, disclose bool) string {
 }
 
 // Models drift into assistant formatting; the chat bubble wants one plain line.
+// Only an actual list marker is removed. Trimming the digit characters
+// themselves ate the number out of every reply that opened with one — "30岁啦"
+// arrived as "岁啦".
+var aiListMarker = regexp.MustCompile(`^(?:[-*•]+\s*|\d{1,2}(?:[.)]\s+|、\s*))`)
+
 func sanitizeAIReply(text string) string {
 	text = strings.TrimSpace(text)
 	if text == "" {
@@ -445,7 +468,7 @@ func sanitizeAIReply(text string) string {
 	text = replacer.Replace(text)
 	lines := []string{}
 	for _, line := range strings.Split(text, "\n") {
-		line = strings.TrimSpace(strings.TrimLeft(strings.TrimSpace(line), "-*•0123456789. "))
+		line = strings.TrimSpace(aiListMarker.ReplaceAllString(strings.TrimSpace(line), ""))
 		if line != "" {
 			lines = append(lines, line)
 		}