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/src/MoShiro.Backend.Api/Admin/AgentEndpoints.cs

@@ -23,7 +23,7 @@ public static class AgentEndpoints
             .Api("agents_get", "One agent", AgentsTag).Returns<AgentDto>().ProducesProblems(401, 403, 404)
             .Requires(Capability.FleetRead);
         group.MapGet("/nodes/{id}/logs", ListNodeLogsAsync)
-            .Api("node_runtime_logs", "Recent runtime logs of a node", "admin-nodes").Returns<NodeRuntimeLogsDto>().ProducesProblems(401, 403)
+            .Api("node_runtime_logs", "Recent runtime logs of a node: pulled from the node when it is online, otherwise what the backend kept", "admin-nodes").Returns<NodeRuntimeLogsDto>().ProducesProblems(401, 403)
             .Requires(Capability.FleetRead);
         group.MapPatch("/agents/{id}", PatchAsync)
             .Accepts<AgentPatchRequest>("application/merge-patch+json", "application/json")
@@ -69,10 +69,13 @@ public static class AgentEndpoints
     private static async Task<IResult> ListAsync(AgentService agents, CancellationToken ct) =>
         TypedResults.Json(new PageDto<AgentDto>([.. (await agents.ListAsync(ct)).Select(Mappers.ToDto)], null), ApiJsonContext.Default.PageDtoAgentDto);
 
-    private static Microsoft.AspNetCore.Http.HttpResults.JsonHttpResult<NodeRuntimeLogsDto> ListNodeLogsAsync(NodeRuntimeLogService logs, string id, int? limit) =>
-        TypedResults.Json(
-            ToDto(logs.List(new NodeId(id), Math.Clamp(limit ?? 100, 1, 200))),
-            ApiJsonContext.Default.NodeRuntimeLogsDto);
+    /// <summary>先向节点拉一次最新的日志（离线或超时就算了），再返回 Backend 里保留的；页面开着时前端每几秒请求一次，就是实时拉取。</summary>
+    private static async Task<IResult> ListNodeLogsAsync(NodeRuntimeLogService logs, string id, int? limit, CancellationToken ct)
+    {
+        var node = new NodeId(id);
+        await logs.PullAsync(node, 100, null, ct);
+        return TypedResults.Json(ToDto(logs.List(node, Math.Clamp(limit ?? 100, 1, 200))), ApiJsonContext.Default.NodeRuntimeLogsDto);
+    }
 
     private static NodeRuntimeLogsDto ToDto(NodeRuntimeLogSnapshot snapshot) =>
         new([.. snapshot.Items.Select(item => new NodeRuntimeLogDto(item.Id, Mappers.Time(item.AtUtcMs), item.Level, item.Message, item.Fields))], snapshot.Dropped);