notation blob sign --force warns about overwriting a signature file that does not exist #1380

What is not working as expected?

notation blob sign --force always prints Warning: existing signature file will be overwritten, even when no signature file exists at the target path. The success output also starts the second line with a stray space.

What did you expect to happen?

The overwrite warning appears only when a signature file already exists, as with notation blob policy import --force and notation blob policy init --force. The success output matches specs/cmd/blob.md:

Successfully signed /tmp/my-blob.bin
Signature file written to /tmp/my-blob.bin.jws.sig

How can we reproduce it?

notation cert generate-test --default test
echo hello > /tmp/my-blob.bin
rm -f /tmp/my-blob.bin.jws.sig
notation blob sign --force /tmp/my-blob.bin

Output:

Warning: existing signature file will be overwritten
Successfully signed /tmp/my-blob.bin
 Signature file written to /tmp/my-blob.bin.jws.sig

Describe your environment

Linux, notation built from main (9ba75db).

What is the version of your Notation CLI or Notation Library?

main at 9ba75db.