Replace BFS traversal that issued 2 SQL queries per folder (list_files +
list_folders) with 2 total queries using PostgreSQL ltree <@ operator:
1. list_subtree_folders: single GiST-indexed scan for all folders
2. list_files_in_subtree: single GiST-indexed join for all files
Files are grouped by folder_id in a HashMap, then iterated in directory
order (folders pre-sorted by path from SQL).
Changes across 4 architecture layers:
- Domain: FolderRepository::list_subtree_folders (default impl)
- Application ports: FolderUseCase, FileRetrievalUseCase, FileReadPort
- Application services: FolderService, FileRetrievalService passthroughs
- Infrastructure: PG implementations + ZipService rewrite
Query count: O(N) → O(1). Latency for 100-folder tree: ~200 round-trips → 3.
Dionisio
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