Backup state stays valid JSON with a name that is not UTF-8; Bin reads on from an id, not a position

lib/Controller/AdminApiController.php

@@ -179,12 +179,12 @@ final class AdminApiController extends Controller {
 		}
 	}
 
-	public function trash(int $targetId, int $offset = 0): JSONResponse {
+	public function trash(int $targetId, string $after = ''): JSONResponse {
 		try {
 			$delay = $this->keys->deleteDelayDays() * 86400;
 			$repo = $this->targets->repository($this->targets->get((string)$targetId));
 			// In parts, so that the page can show how far it is (a read per removed restore point).
-			$page = $repo->trashPage($offset, microtime(true) + self::TRASH_PAGE_SECONDS);
+			$page = $repo->trashPage($after, microtime(true) + self::TRASH_PAGE_SECONDS);
 			$out = [];
 			foreach ($page['items'] as $id => $info) {
 				$out[] = ['id' => $id, 'label' => $info['label'], 'time' => $info['time'], 'removedAt' => $info['forgottenAt'],

lib/Job/BackupRun.php

@@ -62,9 +62,9 @@ final class BackupRun {
 				if (!mb_check_encoding($logical, 'UTF-8') || !Repository::isSafePath($logical)) {
 					// A name a snapshot cannot hold (a backslash, a control character, not UTF-8). One
 					// such path must not make a backup fail, or the whole snapshot unreadable later.
+					// The cursor stays where it is: the state is JSON, which cannot hold such a name. A
+					// next step meets it again, and it is reported once.
 					self::recordUnreadable($state, $stats, mb_scrub($logical, 'UTF-8'));
-					$state['cur'] = null;
-					$state['after'] = $logical;
 					continue;
 				}
 				if (is_dir($path)) {

lib/Repository/Repository.php

@@ -818,15 +818,20 @@ final class Repository {
 
 	/**
 	 * Part of trash(), for a page that shows how far it is: each entry is a read of its own on the
-	 * location. Reads on from $offset until $deadline (microtime(true)), at least one entry.
+	 * location. Reads the entries with an id after $after, in order, until $deadline
+	 * (microtime(true)), at least one. The id, not a position: a cleanup that changes the trash
+	 * between two parts then makes no entry come twice or be missed.
 	 *
 	 * @return array{total: int, items: array<string, array<string, mixed>>}
 	 */
-	public function trashPage(int $offset, float $deadline): array {
+	public function trashPage(string $after, float $deadline): array {
 		$ids = array_map('strval', array_keys($this->catalog->trash));
 		sort($ids, SORT_STRING);
 		$items = [];
-		foreach (array_slice($ids, max(0, $offset)) as $id) {
+		foreach ($ids as $id) {
+			if (strcmp($id, $after) <= 0) {
+				continue;
+			}
 			try {
 				$items[$id] = $this->trashInfo($id);
 			} catch (\Throwable) {