Last piece to connect client to provider: actually downloading the image and displaying it

Client/main/provider.hpp

@@ -1,5 +1,8 @@
 #pragma once
 
+#include "types.hpp"
+#include <cstddef>
+
 // Resolve the Provider's IP and run the device registration + screen fetch
 // test flow. Call once after WiFi is connected.
-void test_provider_communication(void);
+bool test_provider_communication(uint8 *out_buffer, size_t buffer_size);