Struct ProjectionHead 

pub struct ProjectionHead { /* private fields */ }

Re-exported so hotl_engine::ProjectionHead names what SessionHandle::head hands out — the epoch-fenced published projection (commit-protocol.md §Read invariant). It lives in [actor], next to the only thing that may publish it. The projection head the actor publishes (commit-protocol.md §Read invariant, amendment 2): epoch-fenced, published only post-ack, and read by turn tasks through a watch::Receiver they cannot write. The actor is the sole publisher — the watch::Sender never leaves [Head], which only [run] owns.

Implementations

impl ProjectionHead

pub fn leaf(&self) -> Option<&str>

The durable leaf: id of the newest entry applied.

pub fn epoch(&self) -> u64

seq of that entry — the session-global commit order.

pub fn snapshot(&self) -> Snapshot

The snapshot a turn task samples against, as two channels: the durable projection the head already holds, and the ephemeral suffix regenerated per read. The reminder is never spliced into items — not even into a copy of it — so it can never be committed, replayed, double-counted, or (the point of the split) chosen as a cache breakpoint by a serializer that only sees a flat list.

Both fields hand back an Arc the head or the process already holds whenever it can: the common no-todos read allocates nothing at all, which is what keeps “Vec with clone at grant” the cost model §Read invariant priced.