Green: filter isDeleted tombstones out of listCollections

src/client.ts

@@ -155,7 +155,11 @@ export class Client {
         const { collections } = await this.api.getJSON<{
             collections: RawCollection[];
         }>("/collections/v2", { sinceTime: 0 });
-        return collections.map((raw) =>
+        // The sync API keeps returning deleted collections as tombstones
+        // (isDeleted: true); their diff endpoint 404s, so drop them.
+        return collections
+            .filter((raw) => !raw.isDeleted)
+            .map((raw) =>
                 decryptCollection(
                     raw,
                     {