feat: declare every protocol method's direction and enforce it in the router; add the zero-trust design [CI]

Methods, roles and binary channels are declared in one table per plane (node and peer). RpcRouter checks direction, kind and role when handlers are registered, when messages arrive (fleet_protocol_violation, disconnect after repeated violations) and before sending. NodeConnection is split by responsibility.

backend/tests/MoShiro.Backend.Tests/OperationsAndSecurityTests.cs

@@ -168,15 +168,45 @@ public sealed class OperationsAndSecurityTests
         await agent.SendBinaryAsync([200, 1, 2, 3]); // 未知的二进制通道，长度不够一个完整的头部
         await agent.SendBinaryAsync(OutboxFrame.Build(99, Guid.NewGuid(), [1])); // 没有注册的通道
 
-        // 节点不能调用任何“执行”类的方法：Fleet 根本没有这样的路由
+        // 节点不能调用任何“执行”类的方法：这些方法没有声明，是协议违规，直接拒绝
         foreach (string method in new[] { "fleet.exec", "fleet.shell", "moshiro.exec", "moshiro.write_file", "fleet.update" })
         {
             RpcMessage reply = await agent.RequestRawAsync(method);
-            Assert.Equal("fleet_unsupported", reply.Error!.Data!.Code);
+            Assert.Equal("fleet_protocol_violation", reply.Error!.Data!.Code);
         }
 
-        // 连接仍然可用：路由器照常回复
-        Assert.Equal("fleet_unsupported", (await agent.RequestRawAsync("fleet.exec")).Error!.Data!.Code);
+        // 连接仍然可用：违规次数还没到上限，路由器照常回复
+        Assert.Equal("fleet_protocol_violation", (await agent.RequestRawAsync("fleet.exec")).Error!.Data!.Code);
+    }
+
+    [Fact]
+    public async Task ARepeatOffender_IsDisconnected_AndANodeCannotInitiateWhatOnlyTheBackendMay()
+    {
+        await using AgentSimulator agent = await _backend.ConnectAgentAsync();
+        await agent.WaitForTaskSetAsync(s => s.Tasks.Count == Defaults.TaskCount);
+
+        // 节点冒充 Backend 发起只有 Backend 才能发的方法：违规，不是「不支持」
+        Assert.Equal("fleet_protocol_violation", (await agent.RequestRawAsync(MoShiroMethods.TestRun)).Error!.Data!.Code);
+        Assert.Equal("fleet_protocol_violation", (await agent.RequestRawAsync("fleet.state.sync")).Error!.Data!.Code);
+
+        // 一个 Probe 都不是的 Agent 发 Probe 才有的通道：节点面的列块通道（17）没有声明，不会进收件箱
+        await agent.SendBinaryAsync(OutboxFrame.Build(MoShiroChannels.ColumnBlock, Guid.NewGuid(), [1]));
+
+        // 反复违规：超过上限（默认 20 次）之后连接被服务端关闭
+        for (int i = 0; i < 40 && agent.CloseReason is null; i++)
+        {
+            try
+            {
+                await agent.RequestRawAsync("fleet.exec");
+            }
+            catch (Exception ex) when (ex is TimeoutException or OperationCanceledException or System.Net.WebSockets.WebSocketException or InvalidOperationException)
+            {
+                break;
+            }
+        }
+
+        await BackendFixture.EventuallyAsync(() => Task.FromResult(agent.CloseReason is not null), because: "a node that keeps violating the protocol is disconnected");
+        Assert.Equal("protocol violations", agent.CloseReason);
     }
 
     [Fact]