Encrypting a Syncthing volume on OpenBSD with softraid

I run a small OpenBSD box as one of my Syncthing nodes. Unlike my homelab server, I can&rsquo;t fully guarantee its physical security, so if it ever ends up in the wrong hands, I don&rsquo;t want the disk to just sit there with plaintext data on it. The goal was to encrypt the Syncthing data volume and require a passphrase after every reboot before Syncthing can touch it. What didn&rsquo;t work…