Add event-driven state sync with ETag optimization

Infrastructure/StateChangeNotificationMiddleware.cs

@@ -0,0 +1,31 @@
+namespace GameList.Infrastructure;
+
+public sealed class StateChangeNotificationMiddleware(RequestDelegate next)
+{
+    public async Task InvokeAsync(HttpContext context, StateChangeNotifier notifier)
+    {
+        await next(context);
+
+        if (ShouldNotify(context))
+            notifier.NotifyChange();
+    }
+
+    private static bool ShouldNotify(HttpContext context)
+    {
+        if (context.Response.StatusCode >= StatusCodes.Status400BadRequest)
+            return false;
+
+        if (!HttpMethods.IsPost(context.Request.Method)
+            && !HttpMethods.IsPut(context.Request.Method)
+            && !HttpMethods.IsDelete(context.Request.Method))
+            return false;
+
+        var path = context.Request.Path;
+
+        return path.StartsWithSegments("/api/suggestions", StringComparison.OrdinalIgnoreCase)
+            || path.StartsWithSegments("/api/votes", StringComparison.OrdinalIgnoreCase)
+            || path.StartsWithSegments("/api/admin", StringComparison.OrdinalIgnoreCase)
+            || path.StartsWithSegments("/api/me/phase", StringComparison.OrdinalIgnoreCase)
+            || path.StartsWithSegments("/api/auth/register", StringComparison.OrdinalIgnoreCase);
+    }
+}