fix: move simTime into lock, local capture _inner to prevent mid-swap reads

Author: WomB0ComB0

src/ResQ.Viz.Web/Services/SimulationService.cs

@@ -168,13 +168,16 @@ protected override async Task ExecuteAsync(CancellationToken stoppingToken)
     {
         while (!stoppingToken.IsCancellationRequested)
         {
+            bool shouldBroadcast;
             lock (_lock)
             {
                 _world.Step();
                 _tickCount++;
+                _simTime += 1.0 / 60.0;
+                shouldBroadcast = _tickCount % 6 == 0;
             }
 
-            if (_tickCount % 6 == 0)
+            if (shouldBroadcast)
             {
                 FrameReady?.Invoke(this, EventArgs.Empty);
 
@@ -183,8 +186,6 @@ protected override async Task ExecuteAsync(CancellationToken stoppingToken)
                 var frame    = _frameBuilder.Build(snapshot, _simTime);
                 await _hubContext.Clients.All.SendAsync("ReceiveFrame", frame, stoppingToken);
             }
-
-            _simTime += 1.0 / 60.0;
             await Task.Delay(16, stoppingToken);
         }
     }

src/ResQ.Viz.Web/Services/UpdatableWeatherSystem.cs

@@ -43,14 +43,14 @@ public void Update(WeatherConfig config)
         => _inner = new WeatherSystem(config);
 
     /// <inheritdoc/>
-    public double Visibility => _inner.Visibility;
+    public double Visibility { get { var inner = _inner; return inner.Visibility; } }
 
     /// <inheritdoc/>
-    public double Precipitation => _inner.Precipitation;
+    public double Precipitation { get { var inner = _inner; return inner.Precipitation; } }
 
     /// <inheritdoc/>
-    public Vector3 GetWind(double x, double y, double z) => _inner.GetWind(x, y, z);
+    public Vector3 GetWind(double x, double y, double z) { var inner = _inner; return inner.GetWind(x, y, z); }
 
     /// <inheritdoc/>
-    public void Step(double dt) => _inner.Step(dt);
+    public void Step(double dt) { var inner = _inner; inner.Step(dt); }
 }