Add framebuffer content debug check (temp diagnostic)

crates/wrsrvd/src/backend/headless.rs

@@ -268,6 +268,24 @@ fn render_headless_frame(data: &mut CalloopData) {
                 std::slice::from_raw_parts(ptr, frame_bytes)
             };
 
+            // Debug: check if the framebuffer contains anything besides the clear color.
+            if element_count > 0 {
+                // Clear color [0.1, 0.1, 0.1, 1.0] ≈ [25, 25, 25, 255] in u8
+                // Count unique non-bg BGRA values in first 1000 pixels
+                let unique: std::collections::HashSet<[u8; 4]> = pixels
+                    .chunks_exact(4)
+                    .take(1000)
+                    .map(|p| [p[0], p[1], p[2], p[3]])
+                    .collect();
+                tracing::info!(
+                    unique_colors = unique.len(),
+                    first_pixel = ?&pixels[..4.min(pixels.len())],
+                    stride,
+                    total_bytes = pixels.len(),
+                    "framebuffer content check"
+                );
+            }
+
             // Send frame over network if a client is connected.
             if data.client_connected {
                 send_frame_to_network(data, pixels, &damage, output_size.w, output_size.h, stride);