First-pass QR generation: test harmless text at final size

Before generating a production QR code, encode a harmless sample with the same approximate length and character set as the real payload. Export it at the planned dimensions, preserve a quiet zone, and scan it with another device at realistic distance. Compare the decoded text exactly. If the sample fails, adjust size, contrast, or error correction before using the live destination. Then scan the final artifact too; a sample only validates the setup.