• Bolt is normally-open.
• First phase of a progressive trigger drops the bolt, chambering a round. Second phase fires.
• The breech would necessarily be locked, for caseless, therefore we don't have mass lurch like a blowback open-bolt gun. (Edit: don't know what I was thinking when I wrote this)
• Locking system would likely be anything BUT rotating-bolt, as rotating-bolt is high-friction and the only reason to prefer it is primary extraction, which we don't care about with caseless.

The idea is you have bolt holdopen after every shot for cooling.

The second phase of the trigger would likely be an electric switch, and so the mechanism in total amounts to simple open-bolt style.

Perhaps a bolt would smash up the caseless rounds too much. I haven't ever heard of self-loading caseless guns using a bolt.