Read a view over an incomplete GeoParquet index as PARTIAL

The browser's partition index kept whether it was complete only to
schedule a rebuild and handed the partitions on without it, so a view
counted unread partitions from an index that might be missing some and
could read as complete, even empty, over an area it had never indexed.
A view over an incomplete index now reads PARTIAL until a rebuild
completes.

src/library/parquet.test.mjs

@@ -181,6 +181,36 @@ test('a revisit still finds homes at the edge of a partition', async () => {
   assert.equal(outside.features.length, 0);
 });
 
+test('a view over an incomplete index reads PARTIAL', async () => {
+  const home = {
+    type: 'Feature',
+    geometry: { type: 'Point', coordinates: [-1.2, 53.3] },
+    properties: { CURRENT_ENERGY_RATING: 'C', UPRN: '1' },
+  };
+  const visit = (complete) =>
+    createLibrarySource({
+      entries: [epc],
+      fetchImpl: async () => ({ ok: false, status: 404 }),
+      storage: null,
+      loadParquet: async () => ({
+        ...(await import('./parquet.js')),
+        buildPartitionIndex: async () => ({
+          partitions: [
+            { url: 'https://h/A.parquet', bbox: [-1.5, 53.2, -1.1, 53.5] },
+          ],
+          complete,
+        }),
+        readGeoParquetFeatures: async () => [home],
+      }),
+    });
+  const box = [-1.21, 53.29, -1.19, 53.31];
+  const whole = await visit(true).loadDataset(epc, { bbox: box });
+  assert.equal(whole.truncated, false);
+  const partial = await visit(false).loadDataset(epc, { bbox: box });
+  assert.equal(partial.features.length, 1);
+  assert.equal(partial.truncated, true);
+});
+
 test('a footer that keeps failing leaves the index incomplete, and a retry recovers', async () => {
   const { buildPartitionIndex } = await import('./parquet.js');
   const entry = {

src/library/source.js

@@ -236,7 +236,7 @@ export function createLibrarySource({
           current.retryAt = result.complete
             ? null
             : now() + PARTIAL_INDEX_RETRY_MS;
-        return result.partitions;
+        return result;
       },
       (error) => {
         if (indexes.get(entry.id)?.promise === promise)
@@ -283,7 +283,7 @@ export function createLibrarySource({
    * batches until one batch finds features in view.
    */
   async function loadPartitioned(entry, box, { signal }) {
-    const [{ partitionsForBox, featureInBox }, index] = await Promise.all([
+    const [{ partitionsForBox, featureInBox }, built] = await Promise.all([
       loadParquet(),
       partitionIndex(entry, { signal }),
     ]);
@@ -294,7 +294,12 @@ export function createLibrarySource({
     }
     const learned =
       storedJson(storage, `${EXTENT_STORAGE_PREFIX}${entry.id}`) || {};
-    const ranked = rankPartitions(index, box, learned, partitionsForBox);
+    const ranked = rankPartitions(
+      built.partitions,
+      box,
+      learned,
+      partitionsForBox,
+    );
     const candidates = ranked.slice(0, MAX_PARTITION_READS_PER_VIEW);
     // Every partition the box touches but this view leaves unread (the read
     // budget, or the early stop below) makes the result partial.
@@ -327,7 +332,8 @@ export function createLibrarySource({
     });
     return {
       features: bounded.features,
-      truncated: bounded.truncated || unread > 0,
+      // An incomplete index may be missing partitions this box needs.
+      truncated: bounded.truncated || unread > 0 || !built.complete,
     };
   }