Interface SamplingSession<Scores, DeviceToken, Result>

Optional stateless operation shared across compatible rows and positions. It borrows scores and returns owned device tokens, without advancing history.

Optional per-position operation for ONE request whose selection depends on no grammar or probability capture: position p's draw depends only on its scores, its step and its processor history. Borrows [N,V] scores and returns owned device tokens [N] for the given steps, without advancing history. A request with processor history (needsHistory) also passes the window's inputs [N] (borrowed: the pending token, then the drafts): position p reads its history extended by inputs[1..p], the history sample() would hold there had every earlier position drawn its draft. Draws are those sample() would make at each step: seeded sampling keys by (seed, step), never by a shared stream, so unused positions cost nothing. commit takes the tokens a walk over the window used, in order, and advances history as sample() would have advanced it drawing each.

Optional draw left on the device for a request whose selection depends on its processor history but on no grammar or probability capture: borrows [1,V] scores and returns the owned device token sample() would draw at step, committing it to history unread when sample() would commit it.