agent: unify listening and dialing with directed mutual measurements

Replace Probe with Agent across node runtime, Fleet contracts, backend state, API and storage. Report incoming sessions and outgoing link health through each Agent uplink, and retain directed link controls and retry.

Update protocol fixtures and end-to-end coverage for the unified model; accept requested cancellation during the Fleet timeout test cleanup.

backend/agent/tests/MoShiro.Agent.Tests/OpenWrtUpdaterTests.cs

@@ -0,0 +1,52 @@
+using System.Text.Json;
+using Fleet.Core;
+using Fleet.Hosting;
+using MoShiro.Protocol;
+
+namespace MoShiro.Agent.Tests;
+
+public sealed class OpenWrtUpdaterTests : IDisposable
+{
+    private readonly string _directory = Path.Combine(Path.GetTempPath(), "moshiro-native-" + Guid.NewGuid().ToString("N"));
+
+    [Fact]
+    public void Offer_AndApply_WriteFixedFlags_NotRemoteManifestOrCommands()
+    {
+        var updater = new OpenWrtUpdater(_directory, Path.Combine(_directory, "status.json"), TimeProvider.System, NullNodeLog.Instance);
+        updater.Offer();
+        updater.RequestApply();
+        Assert.Equal("check", File.ReadAllText(Path.Combine(_directory, "check.request")));
+        Assert.Equal("check", File.ReadAllText(Path.Combine(_directory, "apply.request")));
+        Assert.Equal(2, Directory.GetFiles(_directory).Length);
+    }
+
+    [Fact]
+    public void Status_WritesHealthAndReadsHostStatus()
+    {
+        var store = new ConfigStore(_directory);
+        store.Write("status.json", "{\"state\":\"rolled_back\",\"at\":123}"u8.ToArray());
+        var updater = new OpenWrtUpdater(_directory, Path.Combine(_directory, "status.json"), TimeProvider.System, NullNodeLog.Instance);
+        Assert.Equal("rolled_back", updater.Status()?.State);
+        using JsonDocument health = JsonDocument.Parse(File.ReadAllBytes(Path.Combine(_directory, "health.json")));
+        Assert.Equal(BuildInfo.Version, health.RootElement.GetProperty("version").GetString());
+        Assert.Equal(Environment.ProcessId, health.RootElement.GetProperty("pid").GetInt32());
+        Assert.True(health.RootElement.GetProperty("at").GetInt64() > 0);
+    }
+
+    [Fact]
+    public void Status_MissingOrCorruptHostStatus_DoesNotStopCollector()
+    {
+        var updater = new OpenWrtUpdater(_directory, Path.Combine(_directory, "status.json"), TimeProvider.System, NullNodeLog.Instance);
+        Assert.Null(updater.Status());
+        new ConfigStore(_directory).Write("status.json", "not json"u8.ToArray());
+        Assert.Null(updater.Status());
+    }
+
+    public void Dispose()
+    {
+        if (Directory.Exists(_directory))
+        {
+            Directory.Delete(_directory, recursive: true);
+        }
+    }
+}