Invoke a synchronous host signer without granting it private-key access.
Provider-thrown Softchat cancellation/rejection errors are preserved; unknown provider failures map to external_signer_rejected.
external_signer_rejected
Invoke a synchronous host signer without granting it private-key access.
Provider-thrown Softchat cancellation/rejection errors are preserved; unknown provider failures map to
external_signer_rejected.