✨ Gateway readiness check

DysonNetwork.Gateway/Health/GatewayReadinessMiddleware.cs

@@ -0,0 +1,35 @@
+namespace DysonNetwork.Gateway.Health;
+
+using Microsoft.AspNetCore.Http;
+
+public sealed class GatewayReadinessMiddleware(RequestDelegate next)
+{
+    public async Task InvokeAsync(HttpContext context, GatewayReadinessStore store)
+    {
+        if (context.Request.Path.StartsWithSegments("/health"))
+        {
+            await next(context);
+            return;
+        }
+
+        var readiness = store.Current;
+
+        // Only core services participate in readiness gating
+        var notReadyCoreServices = readiness.Services
+            .Where(kv => GatewayConstant.CoreServiceNames.Contains(kv.Key))
+            .Where(kv => !kv.Value.IsHealthy)
+            .Select(kv => kv.Key)
+            .ToArray();
+
+        if (notReadyCoreServices.Length > 0)
+        {
+            context.Response.StatusCode = StatusCodes.Status503ServiceUnavailable;
+            var unavailableServices = string.Join(", ", notReadyCoreServices);
+            context.Response.Headers["X-NotReady-Services"] = unavailableServices;
+            await context.Response.WriteAsync("Solar Network is warming up. Try again later please.");
+            return;
+        }
+
+        await next(context);
+    }
+}