A rebuilt manifest leaves out every entry whose files are missing on that machine, so a run
with failed downloads silently dropped entries from the tracked file (PR #7 carried one 42
audio entries short; all 42 still resolve upstream). The run now keeps the current manifest,
prints the entries it would drop (also in the report) and exits 1. The tool runs main only as
a script so the guard and parseArgs can be tested; ASSETS.md documents the flag.
sganggs