Function load_store_for 

pub fn load_store_for(
    path: &Path,
    before_ms: Option<i64>,
    session: Option<&str>,
) -> Vec<Challenge>

load_for with this engineer’s personal lessons of the same store (reach.rs PERSONAL_FILE, beside path) over the team’s: what a session of this collective is delivered. A personal lesson replaces its tombstone and is delivered like a team lesson, for this file is this machine’s alone and this store this collective’s alone. Costs one open more, a read only when the file exists.