第二阶段优化已完成，重点是提高后台任务吞吐并降低 Outbox 数据库开销。

RabbitMQ 默认从单一回调通道提升为三类任务独立并行，跨类型并发能力由 1 提升到 3；每类还能独立配置 1–16 个消费者。[RabbitMqBackgroundJobs.cs (line 143)](E:/jiaowu/src/Jiaowu.Api/Infrastructure/BackgroundJobs/RabbitMqBackgroundJobs.cs:143)
InMemory 开发模式同步改为按任务类型隔离队列，避免某类长任务堵塞其他任务。
租约恢复检查从“每发布一条执行一次”改为默认每 60 秒维护一次。
启动恢复改为数据库 NOT EXISTS 查询，不再把全部历史 Outbox 加载进内存。[BackgroundJobOutboxPublisher.cs (line 9)](E:/jiaowu/src/Jiaowu.Api/Infrastructure/BackgroundJobs/BackgroundJobOutboxPublisher.cs:9)
完成消息默认保留 14 天，之后按每批 500 条清理，并增加对应组合索引。
/health/messaging 现在返回各状态积压量、过期租约和最老任务等待时间。[BackgroundJobMonitoringService.cs (line 16)](E:/jiaowu/src/Jiaowu.Api/Infrastructure/BackgroundJobs/BackgroundJobMonitoringService.cs:16)
新增 Jiaowu.BackgroundJobs 运行时指标，覆盖发布量、处理量、发布耗时、处理耗时和清理量。[BackgroundJobTelemetry.cs (line 9)](E:/jiaowu/src/Jiaowu.Api/Infrastructure/BackgroundJobs/BackgroundJobTelemetry.cs:9)
配置、Compose 和调优建议已更新。[README.md (line 257)](E:/jiaowu/README.md:257)

src/Jiaowu.Api/Infrastructure/BackgroundJobs/InMemoryBackgroundJobWorker.cs

@@ -1,27 +1,46 @@
+using Jiaowu.Api.Domain.System;
+
 namespace Jiaowu.Api.Infrastructure.BackgroundJobs;
 
 public sealed class InMemoryBackgroundJobWorker(
     InMemoryBackgroundJobTransport transport,
     BackgroundJobRunner runner,
+    BackgroundJobOptions options,
     ILogger<InMemoryBackgroundJobWorker> logger) : BackgroundService
 {
     protected override async Task ExecuteAsync(CancellationToken stoppingToken)
     {
+        var workers = Enum.GetValues<BackgroundJobKind>()
+            .SelectMany(kind => Enumerable.Range(
+                    0,
+                    options.ConsumerConcurrency(kind))
+                .Select(_ => ConsumeAsync(kind, stoppingToken)))
+            .ToArray();
+
         try
         {
-            await foreach (var message in transport.ReadAllAsync(stoppingToken))
-            {
-                var result = await runner.RunAsync(message, stoppingToken);
-                if (result.Outcome != BackgroundJobRunOutcome.Retry)
-                    continue;
-
-                await Task.Delay(result.RetryAfter, stoppingToken);
-                await transport.PublishAsync(message, stoppingToken);
-            }
+            await Task.WhenAll(workers);
         }
         catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
         {
             logger.LogInformation("In-memory background job worker is stopping.");
         }
     }
+
+    private async Task ConsumeAsync(
+        BackgroundJobKind kind,
+        CancellationToken cancellationToken)
+    {
+        await foreach (var message in transport.ReadAllAsync(
+                           kind,
+                           cancellationToken))
+        {
+            var result = await runner.RunAsync(message, cancellationToken);
+            if (result.Outcome != BackgroundJobRunOutcome.Retry)
+                continue;
+
+            await Task.Delay(result.RetryAfter, cancellationToken);
+            await transport.PublishAsync(message, cancellationToken);
+        }
+    }
 }