1. add --progress BooleanOptionalAction flag with plain mode;
2. progress_t tracks total/done/this_run packages and bytes, shows ETA and rate;
3. rate displayed as pkg/s when fast, s/pkg when slow;
4. add -j parameter for parallel downloads via ThreadPoolExecutor;
5. for aria2c with -j>1, use download_batch_aria2c with single process and input file;
6. skip already-downloaded files, estimate total bytes from average;
7. add test_download_cli.py with full test matrix: backend(3) x jobs(2) x progress(2) x existing(3);
8. mock downloader_t.download and download_batch_aria2c in all tests;
9. add unit tests for progress_t formatting and batch aria2c input generation;
LLM
15df281e61