Roadmap: phase A done 9d333fc9ca1b

            .filter(|(l, a)| a.is_some() && *l != lane && !edges.iter().any(|e| e.1 == *l))

            .map(|(l, _)| l)

            .collect();

        while active.last().is_some_and(|a| a.is_none()) {

            active.pop();

        }

/// The number of lanes the rows use.

pub fn width(rows: &[Row]) -> usize {

    rows.iter()

        .max()

        .map(|m| m + 1)

        .unwrap_or(1)

    #[test]

    fn a_diamond_takes_two_lanes_and_rejoins() {

        assert_eq!(rows[0].edges, vec![(0, 0), (0, 1)]);

        assert_eq!(rows[2].lane, 1);

        assert_eq!(width(&rows), 2);

    }

}

    /// A window of `log_state`: entries `offset..offset+limit` and the total

    /// count, for paginated views.

        let all = self.log_state(heads)?;

        let total = all.len();

        Ok((all.into_iter().skip(offset).take(limit).collect(), total))

    self as o, AtomRef, Change, ChangeKind, Edit, Hlc, Mode, NodeKind, ObjectError, TreeOp,

};

use crate::tree::{TreeGraph, TreeView};

use std::sync::{Arc, Mutex};

#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]

pub enum StateError {

## Progress