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/Program.cs

@@ -137,7 +137,13 @@ if (!backgroundJobOptions.Transport.Equals(
 if (backgroundJobOptions.PollIntervalMilliseconds is < 100 or > 30000 ||
     backgroundJobOptions.LeaseSeconds is < 30 or > 3600 ||
     backgroundJobOptions.PrefetchCount is < 1 or > 100 ||
+    backgroundJobOptions.AutomaticScheduleConcurrency is < 1 or > 16 ||
+    backgroundJobOptions.SchedulePublishConcurrency is < 1 or > 16 ||
+    backgroundJobOptions.MakeupExamAutoConcurrency is < 1 or > 16 ||
     backgroundJobOptions.ProcessingAttemptLimit is < 1 or > 100 ||
+    backgroundJobOptions.MaintenanceIntervalSeconds is < 10 or > 3600 ||
+    backgroundJobOptions.CompletedRetentionDays is < 1 or > 3650 ||
+    backgroundJobOptions.CleanupBatchSize is < 10 or > 5000 ||
     string.IsNullOrWhiteSpace(backgroundJobOptions.Exchange) ||
     string.IsNullOrWhiteSpace(backgroundJobOptions.QueuePrefix))
 {
@@ -269,6 +275,8 @@ builder.Services.AddScoped<ExamArrangementService>();
 builder.Services.AddScoped<MakeupExamEligibilityService>();
 builder.Services.AddScoped<MakeupExamArrangementService>();
 builder.Services.AddScoped<MakeupExamAutoJobProcessor>();
+builder.Services.AddSingleton<BackgroundJobTelemetry>();
+builder.Services.AddScoped<BackgroundJobMonitoringService>();
 builder.Services.AddSingleton<BackgroundJobRunner>();
 if (backgroundJobOptions.UsesRabbitMq)
 {
@@ -534,15 +542,41 @@ static async Task<IResult> CheckCacheHealthAsync(
 
 static async Task<IResult> CheckMessagingHealthAsync(
     IBackgroundJobTransport transport,
+    BackgroundJobMonitoringService monitoring,
     CancellationToken cancellationToken)
 {
     var healthy = await transport.CheckHealthAsync(cancellationToken);
     var backend = transport.IsDurable ? "rabbitmq" : "memory";
-    return healthy
-        ? Results.Ok(new { Status = "healthy", Backend = backend })
-        : Results.Json(
-            new { Status = "unhealthy", Backend = backend },
+    try
+    {
+        var backlog = await monitoring.GetSnapshotAsync(cancellationToken);
+        return healthy
+            ? Results.Ok(new
+            {
+                Status = "healthy",
+                Backend = backend,
+                Backlog = backlog
+            })
+            : Results.Json(
+                new
+                {
+                    Status = "unhealthy",
+                    Backend = backend,
+                    Backlog = backlog
+                },
+                statusCode: StatusCodes.Status503ServiceUnavailable);
+    }
+    catch
+    {
+        return Results.Json(
+            new
+            {
+                Status = "unhealthy",
+                Backend = backend,
+                Backlog = (object?)null
+            },
             statusCode: StatusCodes.Status503ServiceUnavailable);
+    }
 }
 
 public partial class Program;