I've seen a few sentences like
Estoy a salvo
Estoy a gusto
But the fact that "a" is required in these sentences surprised me.
It doesn't seem like "estoy" + past participle always requires "a" in between, for example:
At first I thought the difference is because "salvo" and "gusto" are transitive verbs and I'm the direct object. But "aburrir" and "cansar" are also transitive. Perhaps "aburrir" and "cansar" are used here in the passive voice, but "salvar" and "gustar" are not passive in the above examples?