fleet: require a minimum version of the peer at the handshake [CI]

MoShiro__MinAgentVersion makes the backend refuse agents below it at hello (fleet_version_required); fleet.min_server_version or MOSHIRO_MIN_SERVER_VERSION makes the agent drop a backend below it. Either side waits five seconds and shakes hands again, because the other one may be updating.

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

@@ -0,0 +1,72 @@
+using System.Text.Json;
+using Fleet.Core;
+using Fleet.Rpc;
+using Microsoft.Extensions.DependencyInjection;
+using MoShiro.Backend.Application;
+using MoShiro.TestSupport;
+
+namespace MoShiro.Backend.Tests;
+
+public sealed class VersionRequirementTests : IClassFixture<BackendFixture>
+{
+    private readonly BackendFixture _backend;
+
+    public VersionRequirementTests(BackendFixture backend)
+    {
+        _backend = backend;
+    }
+
+    [Fact]
+    public async Task AnAgentBelowTheRequiredVersion_IsRejectedAtHello_AndGetsInOnceTheRequirementIsMet()
+    {
+        BackendOptions options = _backend.App.Services.GetRequiredService<BackendOptions>();
+        options.MinAgentVersion = "9.0.0"; // 模拟器的版本是 0.0.1-sim
+        try
+        {
+            await using AgentSimulator old = await _backend.ConnectAgentAsync(hello: false);
+            var hello = new HelloParams { NodeVersion = "0.0.1-sim", NowUtcMs = TimeProvider.System.GetUtcNow().ToUnixTimeMilliseconds() };
+            RpcMessage reply = await old.RequestRawAsync(FleetMethods.Hello, JsonSerializer.SerializeToElement(hello, FleetRpcContext.Default.HelloParams));
+            Assert.Equal(FleetErrors.VersionRequired.Value, reply.Error!.Data!.Code);
+            Assert.Contains("9.0.0", reply.Error.Message);
+        }
+        finally
+        {
+            options.MinAgentVersion = null; // 共用的后端：恢复，别影响别的测试
+        }
+
+        await using AgentSimulator ok = await _backend.ConnectAgentAsync();
+        Assert.True(_backend.App.Services.GetRequiredService<MoShiro.Backend.Application.IAgentGateway>().IsOnline(ok.NodeId));
+    }
+
+    [Fact]
+    [Trait("Category", "Slow")]
+    public async Task AnAgentTheBackendRejectedForItsVersion_TriesAgainEveryFiveSeconds_AndComesOnlineWhenAccepted()
+    {
+        BackendOptions options = _backend.App.Services.GetRequiredService<BackendOptions>();
+        IAgentGateway gateway = _backend.App.Services.GetRequiredService<IAgentGateway>();
+        options.MinAgentVersion = "999.0.0";
+        try
+        {
+            await using AgentHarness agent = await AgentHarness.StartAsync(_backend, waitForConnection: false);
+            await Task.Delay(TimeSpan.FromSeconds(2));
+            Assert.False(gateway.IsOnline(agent.NodeId));
+
+            options.MinAgentVersion = null; // 通过了：下一次握手（最迟 5 秒）就上线
+            await BackendFixture.EventuallyAsync(() => Task.FromResult(gateway.IsOnline(agent.NodeId)), TimeSpan.FromSeconds(12));
+        }
+        finally
+        {
+            options.MinAgentVersion = null;
+        }
+    }
+
+    [Fact]
+    [Trait("Category", "Slow")]
+    public async Task AnAgentThatRequiresANewerBackend_DoesNotGoOnline_AndKeepsChecking()
+    {
+        IAgentGateway gateway = _backend.App.Services.GetRequiredService<IAgentGateway>();
+        await using AgentHarness agent = await AgentHarness.StartAsync(_backend, config => config.Fleet.MinServerVersion = "999.0.0", waitForConnection: false);
+        await Task.Delay(TimeSpan.FromSeconds(7)); // 至少重试过一次
+        Assert.False(gateway.IsOnline(agent.NodeId));
+    }
+}