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/src/MoShiro.Backend.Application/Updates/ReleaseService.cs

@@ -11,7 +11,7 @@ namespace MoShiro.Backend.Application;
 public sealed record ReleaseOffer(string Component, long Seq, string Tag, string Version, string Digest, string Manifest, string Signature, string Channel = "release");
 
 /// <summary>
-/// 发布清单的分发：CI 签名之后推给面板，面板存下来并原样转给在线的 Agent、Probe（节点连上时再补发一次）。
+/// 发布清单的分发：CI 签名之后推给面板，面板存下来并原样转给在线的节点（节点连上时再补发一次）。
 /// 登记入口（<c>/api/release/offer</c>）只收带有效 CI 签名的清单；面板<b>不决定拉什么</b>：节点宿主机上的更新器用本机的发布公钥验签，并且只认本机配置的镜像仓库；
 /// 所以面板即使被攻破，也推不出一个能被装上的假镜像。面板只负责「通知」和「请求更新」，状态由节点随心跳报回来。
 /// </summary>
@@ -20,7 +20,8 @@ public sealed partial class ReleaseService : IDisposable
     public const int MaxManifestBytes = 4096;
     public const int MaxSignatureBytes = 512;
     public const string BackendComponent = "backend";
-    private static readonly string[] s_components = [NodeKinds.Agent, NodeKinds.Probe, BackendComponent];
+    public const string AgentComponent = "agent";
+    private static readonly string[] s_components = [AgentComponent, BackendComponent];
 
     private readonly ISettingsStore _settings;
     private readonly IAgentGateway _gateway;
@@ -116,7 +117,7 @@ public sealed partial class ReleaseService : IDisposable
     /// <summary>不再信任某把密钥之后（删除自有发布密钥）：已登记的清单里，现在验不过的丢掉，免得继续分发。</summary>
     public async ValueTask PurgeUnverifiedAsync(CancellationToken ct)
     {
-        foreach (string key in new[] { NodeKinds.Agent, NodeKinds.Probe, BackendComponent + ".dev", BackendComponent + ".release" })
+        foreach (string key in new[] { AgentComponent, BackendComponent + ".dev", BackendComponent + ".release" })
         {
             string? manifest = await _settings.GetAsync(Key(key, "manifest"), ct);
             string? signature = await _settings.GetAsync(Key(key, "signature"), ct);
@@ -188,9 +189,7 @@ public sealed partial class ReleaseService : IDisposable
     private IEnumerable<NodeId> OnlineOf(string component) => _gateway.OnlineNodes.Where(n => ComponentOf(n) == component);
 
     internal static string? ComponentOf(NodeId node) =>
-        node.Value.StartsWith(AgentIds.Prefix, StringComparison.Ordinal) ? NodeKinds.Agent
-        : node.Value.StartsWith(ProbeId.Prefix, StringComparison.Ordinal) ? NodeKinds.Probe
-        : null;
+        node.Value.StartsWith(AgentIds.Prefix, StringComparison.Ordinal) ? AgentComponent : null;
 
     private static string Key(string component, string part) => $"release.{component}.{part}";