Function load_materialized_projection_tail 

pub fn load_materialized_projection_tail(
    session_id: &str,
    transcript_limit: usize,
) -> Result<Option<(MaterializedSession, ProjectionWindow)>>

Load a projection carrying only the end of its transcript.

The steady-state poll reloads a session’s projection every time anything about it moves. Loading the whole transcript to do that is work proportional to everything that has ever happened in the conversation — 635 MiB and 28,066 items on one measured session — for a view that shows the last few hundred entries. This reads the window instead, plus the two facts that live outside it, each with one indexed query. See ProjectionWindow.