Read an ArcGIS load stopped at maxFeatures as truncated

Paging stopped once maxFeatures were read before it noted that the
upstream had more, so a page holding exactly the cap with
exceededTransferLimit set read as the whole dataset. FEMA USA
Structures (2,000 features, one page) never showed PARTIAL in a dense
view. Stopping at the cap or the last page with more upstream now marks
the load truncated.

src/library/formats.js

@@ -429,8 +429,15 @@ export async function loadLibraryDataset(
       const parsed = parseLibraryBody('arcgis', await readPage(url, budget));
       candidates.push(...parsed.candidates);
       if (!parsed.exceededTransferLimit || !parsed.candidates.length) break;
-      if (candidates.length >= source.maxFeatures) break;
-      if (page === source.maxPages - 1) truncated = true;
+      // The upstream holds more than was read: stopping here, at the
+      // feature cap or the last page, leaves the dataset partial.
+      if (
+        candidates.length >= source.maxFeatures ||
+        page === source.maxPages - 1
+      ) {
+        truncated = true;
+        break;
+      }
     }
   } else {
     const parsed = parseLibraryBody(

src/library/formats.test.mjs

@@ -182,6 +182,27 @@ test('ArcGIS paging follows exceededTransferLimit up to maxPages', async () => {
   assert.equal(collection.truncated, true);
 });
 
+test('ArcGIS stopping at maxFeatures with more upstream reads as truncated', async () => {
+  const value = entry({
+    format: 'arcgis',
+    url: 'https://s.example.org/FeatureServer/0',
+    maxFeatures: 3,
+    maxPages: 5,
+  });
+  let pages = 0;
+  const collection = await loadLibraryDataset(value, async () => {
+    pages += 1;
+    return JSON.stringify({
+      type: 'FeatureCollection',
+      properties: { exceededTransferLimit: true },
+      features: [point(1, 0), point(2, 0), point(3, 0)],
+    });
+  });
+  assert.equal(pages, 1);
+  assert.equal(collection.features.length, 3);
+  assert.equal(collection.truncated, true);
+});
+
 test('a plain dataset request carries the manifest query once', async () => {
   const value = entry({
     format: 'geojson',