排课计算、课表发布、补考自动编排三类任务统一接入消息系统。

业务任务与 Outbox 消息同一事务落库，避免“数据库成功但消息没发出去”。
RabbitMQ 使用持久化消息、发布确认、手动 ACK、Quorum Queue、死信队列。
增加处理租约、心跳、异常重试、最大重试次数和幂等状态控制。
保留 InMemory 模式，开发环境无需安装 RabbitMQ。
支持多实例竞争消费，后续可以横向扩容。
新增 /health/messaging 消息系统健康检查。

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

@@ -0,0 +1,46 @@
+using System.Threading.Channels;
+using Jiaowu.Api.Domain.System;
+
+namespace Jiaowu.Api.Infrastructure.BackgroundJobs;
+
+public sealed record BackgroundJobEnvelope(
+    Guid OutboxMessageId,
+    BackgroundJobKind JobKind,
+    Guid JobId);
+
+public interface IBackgroundJobTransport
+{
+    bool IsDurable { get; }
+
+    ValueTask PublishAsync(
+        BackgroundJobEnvelope message,
+        CancellationToken cancellationToken);
+
+    Task<bool> CheckHealthAsync(CancellationToken cancellationToken);
+}
+
+public sealed class InMemoryBackgroundJobTransport : IBackgroundJobTransport
+{
+    private readonly Channel<BackgroundJobEnvelope> _channel =
+        Channel.CreateBounded<BackgroundJobEnvelope>(
+            new BoundedChannelOptions(256)
+            {
+                FullMode = BoundedChannelFullMode.Wait,
+                SingleReader = true,
+                SingleWriter = false
+            });
+
+    public bool IsDurable => false;
+
+    public ValueTask PublishAsync(
+        BackgroundJobEnvelope message,
+        CancellationToken cancellationToken) =>
+        _channel.Writer.WriteAsync(message, cancellationToken);
+
+    public Task<bool> CheckHealthAsync(CancellationToken cancellationToken) =>
+        Task.FromResult(true);
+
+    public IAsyncEnumerable<BackgroundJobEnvelope> ReadAllAsync(
+        CancellationToken cancellationToken) =>
+        _channel.Reader.ReadAllAsync(cancellationToken);
+}