fleet: send log counters in heartbeats and pull the text on demand

Heartbeats carry per-level counts, the most frequent log types (a stable hash of the message) and the newest id, no text. The node keeps its last 2048 lines; moshiro.logs.fetch lets the backend pull them. The log page pulls when it is open, and the backend pulls warnings and errors once a minute after a node reports an error.

backend/tests/MoShiro.TestSupport/AgentSimulator.cs

@@ -17,6 +17,11 @@ namespace MoShiro.TestSupport;
 /// </summary>
 public sealed class AgentSimulator : IAsyncDisposable
 {
+    /// <summary>节点上保留的日志（<c>moshiro.logs.fetch</c> 按编号返回它们）和收到的拉取请求。</summary>
+    public System.Collections.Concurrent.ConcurrentBag<LogEntryDto> Logs { get; } = [];
+
+    public System.Collections.Concurrent.ConcurrentQueue<LogsFetchParams> LogFetches { get; } = new();
+
     private readonly NodeIdentity _identity;
     private readonly NodeIdentity _tlsKey;
     private readonly ClientWebSocket _socket = new();
@@ -446,6 +451,13 @@ public sealed class AgentSimulator : IAsyncDisposable
                     await SendAsync(RpcMessage.Failure(message.Id, new FleetError(new ErrorCode(errorCode ?? "test_busy"), "refused")));
                 }
 
+                break;
+            case MoShiroMethods.LogsFetch:
+                LogsFetchParams fetch = message.Params!.Value.Deserialize(MoShiroJsonContext.Default.LogsFetchParams)!;
+                LogFetches.Enqueue(fetch);
+                var page = new LogsFetchResult { LastId = Logs.IsEmpty ? 0 : Logs.Max(l => l.Id) };
+                page.Items.AddRange(Logs.Where(l => l.Id > fetch.AfterId).OrderBy(l => l.Id).Take(Math.Max(1, fetch.Limit)));
+                await SendAsync(RpcMessage.Success(message.Id!.Value, page, MoShiroJsonContext.Default.LogsFetchResult));
                 break;
             case MoShiroMethods.TestCancel:
                 TestCancelParams cancel = message.Params!.Value.Deserialize(MoShiroJsonContext.Default.TestCancelParams)!;