perf(tests): isolate network E2E and await QUIC cleanup

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

@@ -0,0 +1,36 @@
+using System.Text.Json.Nodes;
+using MoShiro.Measurement;
+using MoShiro.Protocol;
+using MoShiro.TestSupport;
+
+namespace MoShiro.Backend.Tests;
+
+/// <summary>Exercises the complete Backend → Agent → Probe desired task update with an isolated Backend fixture.</summary>
+[Trait("Category", "Slow")]
+public sealed class AgentTaskSetEndToEndTests : IClassFixture<BackendFixture>
+{
+    private readonly BackendFixture _backend;
+
+    public AgentTaskSetEndToEndTests(BackendFixture backend)
+    {
+        _backend = backend;
+    }
+
+    [Fact]
+    public async Task LineTaskSet_FollowsTheDesiredState_AndIsPushedToTheProbe()
+    {
+        await using AgentHarness agent = await AgentHarness.StartAsync(_backend);
+        await agent.OverrideLineTasksAsync(rateHz: 30);
+        await using ProbeSimulator probe = await agent.ConnectProbeAsync();
+        LineTask udp = (await probe.WaitForTasksAsync(s => s.Tasks.Any(t => t.Kind == "udp_echo" && t.Port == agent.App.QuicPorts[0])))
+            .Tasks.Single(t => t.Kind == "udp_echo");
+
+        JsonNode tasks = await _backend.GetJsonAsync(_backend.Admin, "/api/admin/tasks");
+        JsonNode mine = tasks["items"]!.AsArray().Single(t => t!["agent_id"]?.GetValue<string>() == agent.Id && t["kind"]!.GetValue<string>() == "udp_echo")!;
+        using HttpResponseMessage disabled = await _backend.Admin.PatchAsync("/api/admin/tasks/" + mine["id"]!.GetValue<string>(), BackendFixture.Json(new JsonObject { ["enabled"] = false }, "application/merge-patch+json"));
+        disabled.EnsureSuccessStatusCode();
+
+        LineTaskSet next = await probe.WaitForTasksAsync(s => s.Tasks.All(t => t.Kind != "udp_echo") && s.Version > 0);
+        Assert.DoesNotContain(next.Tasks, t => t.Id == udp.Id);
+    }
+}