feat(backend): generic settings RPC bridge, LogStreamHub SignalR, and log ringbuffer

FinlyticBackend/Hubs/LogStreamHub.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.SignalR;
+using Microsoft.Extensions.Logging;
+
+namespace FinlyticBackend.Hubs;
+
+/// <summary>
+/// SignalR Hub that streams live log messages from microservices to connected web UI clients.
+/// </summary>
+public class LogStreamHub : Hub
+{
+    private readonly ILogger<LogStreamHub> _logger;
+
+    public LogStreamHub(ILogger<LogStreamHub> logger)
+    {
+        _logger = logger;
+    }
+
+    public async Task JoinServiceLogs(string serviceName)
+    {
+        if (!string.IsNullOrWhiteSpace(serviceName))
+        {
+            await Groups.AddToGroupAsync(Context.ConnectionId, serviceName);
+            _logger.LogInformation("[LogStreamHub] Client {ConnectionId} joined log stream for {ServiceName}", Context.ConnectionId, serviceName);
+        }
+    }
+
+    public async Task LeaveServiceLogs(string serviceName)
+    {
+        if (!string.IsNullOrWhiteSpace(serviceName))
+        {
+            await Groups.RemoveFromGroupAsync(Context.ConnectionId, serviceName);
+            _logger.LogInformation("[LogStreamHub] Client {ConnectionId} left log stream for {ServiceName}", Context.ConnectionId, serviceName);
+        }
+    }
+
+    public override async Task OnConnectedAsync()
+    {
+        _logger.LogInformation("[LogStreamHub] Client connected: {ConnectionId}", Context.ConnectionId);
+        await base.OnConnectedAsync();
+    }
+
+    public override async Task OnDisconnectedAsync(Exception? exception)
+    {
+        _logger.LogInformation("[LogStreamHub] Client disconnected: {ConnectionId}", Context.ConnectionId);
+        await base.OnDisconnectedAsync(exception);
+    }
+}