macOS Keychain Error -25294 (errSecNoSuchKeychain) — Fixed by Importing the Certificate into login

You try to import a certificate into your keychain and get error -25294, which blocks the import. errSecNoSuchKeychain, meaning 'the specified keychain could not be found,' almost always points not at the certificate itself but at the destination keychain. Based on a case where switching the import target from Local Items to login fixed it, here is the cause and the shortest path to a fix.