THE EDIT LAB

import {
  EditWorkspace, curveFeaturesToInputs,
} from '@devtomorrow/sundial/edit';

const ws = new EditWorkspace(
  curveFeaturesToInputs(
    deeds,                       // Esri curveRings, arcs intact
    (f) => `parcel ${f.properties.id}`,
  ),
  44.08,                         // reference latitude
  { rules: [floodway] },         // your rules (below)
);

ws.invariants();  // DCEL health, signed-area zero

const hit = ws.snap(lngLat, 6);   // node | edge | null
if (hit?.kind === 'node') {
  const violations = ws.moveVertex(hit.node, to);
  if (violations.length) ws.undo();  // exact, to
}                                    // the last ulp

for (const v of ws.validate()) {
  v.rule;     // 'gap' | 'overlap' |
              // 'self-intersection' | yours
  v.detail;   // "“parcel 3715…”: boundary …"
  v.at;       // [lng, lat] for the map badge
  v.hint;     // the recovery, as an action
}

import {
  WORLD, DEAD, type CustomRule,
} from '@devtomorrow/sundial/edit';

const floodway: CustomRule = {
  id: 'floodway',
  check(t, faces) {
    const out = [];
    for (let f = 0; f < t.faceCount; f++) {
      if (faces && !faces.has(f)) continue;
      if (t.faceFeature[f] === WORLD) continue;
      if (t.heFace[t.faceEdge[f]] === DEAD) continue;
      for (const n of ringNodes(t, f)) {
        if (inMyLayer(t.nodeX[n], t.nodeY[n])) {
          out.push({
            rule: 'floodway',
            detail:
              `${t.featureName(t.faceFeature[f])}: ` +
              'boundary enters the floodway',
            faces: [f],
            at: t.toLngLat(t.nodeX[n], t.nodeY[n]),
            hint: 'press U to undo the move',
          });
          break;
        }
      }
    }
    return out;
  },
};

for (const v of ws.validate()) {
  if (v.rule === 'gap' && v.features) {
    ws.sealGap(v.features[0], v.features[1]);
  }
}

const r = ws.mergeFeatures(keepId, goneId);
if (!r.ok) console.log(r.reason);
// "features 3 and 7 share no boundary line,
//  merge needs adjacency"

import { bufferPoint, bufferPolyline }
  from '@devtomorrow/sundial/edit';

// One true circle, four quarter arcs.
const circle = bufferPoint(clickLngLat, 25, frame);

// Offset sides, 180° end caps, round joins.
const corridor = bufferPolyline(sketch, 8, frame);
// Both export as curveRings, never densified.

map.on('click', (ev) => {
  if (!ev.feature) return;
  // The id-buffer resolves the deed under
  // the cursor in < 2 ms, no geometry scan.
  openPanel(ev.feature.properties);
});

const features = ws.export();
// → [{ id, label?, rings: [{ pts, arcs, hole }] }]

// A sealed fabric rebuilds into TRUE shared
// structure, coincident coordinates weld.
const next = new EditWorkspace(features, 44.08);