Three tasks for spec 0068: (1) derive_position_events + r_col DIRECTION/SIZE
consts + crate-root re-export + report.rs unit tests (reversal, normal lifecycle,
short, window-end open, empty, monotonic position_id); (2) stage1_r_e2e.rs
lockstep-guard direction pin + an agreement E2E folding both summarize_r and
derive_position_events over one recorded ledger; (3) full workspace
build/test/clippy verification. Purely additive — no existing output touched.
refs #115
Brummel
1647737baa