With --output, secret encrypt and secret decrypt emptied that file before
reading any input, so a failed command left it empty, and encrypting a file
onto itself gave the encryption of nothing.
With --output they now hold the result in memory and open --output, with the
same call as before, only once encryption or decryption has succeeded. A
failed command leaves --output untouched, and --input can be the same file.
Without --output the result still goes to stdout as it is produced.
Model: opus-5-5
