When the vault cannot be opened through its current unlocker, the error
now ends by saying that the vault still opens with its mnemonic, and
that 'secret unlocker add passphrase' run with SB_SECRET_MNEMONIC set
gives it a new unlocker; only when the vault metadata records the key
the mnemonic derives. 'secret encrypt' and 'secret decrypt' read the key
secret through vault.GetSecret, as 'secret get' does, so they say it
too. An unreadable 'current' file's error names 'secret version list'
and 'secret version promote'. Causes stay wrapped.
Model: opus-5-5
