M2: local cache of pack indexes (ngb_index)

Opening a repository lists index/ once and downloads only index files
that are not cached; packs written by this server are cached on write,
stale cache rows are dropped. Each resumable step therefore no longer
downloads every index file from the location.

lib/Migration/Version000002Date20261002010000.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+// SPDX-FileCopyrightText: 2026 Dillard Blom
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+namespace OCA\NgBackup\Migration;
+
+use Closure;
+use OCP\DB\ISchemaWrapper;
+use OCP\DB\Types;
+use OCP\Migration\IOutput;
+use OCP\Migration\SimpleMigrationStep;
+
+/** Local cache of the per-pack index files, so opening a repository does not download them all. */
+class Version000002Date20261002010000 extends SimpleMigrationStep {
+	public function changeSchema(IOutput $output, Closure $schemaClosure, array $options): ?ISchemaWrapper {
+		/** @var ISchemaWrapper $schema */
+		$schema = $schemaClosure();
+		if (!$schema->hasTable('ngb_index')) {
+			$t = $schema->createTable('ngb_index');
+			$t->addColumn('id', Types::BIGINT, ['autoincrement' => true, 'notnull' => true, 'unsigned' => true]);
+			$t->addColumn('repository_id', Types::STRING, ['notnull' => true, 'length' => 32]);
+			$t->addColumn('pack_id', Types::STRING, ['notnull' => true, 'length' => 32]);
+			// Plain JSON list of blob entries. Blob ids are keyed hashes and reveal no content.
+			$t->addColumn('entries', Types::TEXT, ['notnull' => true]);
+			$t->setPrimaryKey(['id']);
+			$t->addUniqueIndex(['repository_id', 'pack_id'], 'ngb_index_repo_pack');
+		}
+		return $schema;
+	}
+}