- download_content_many now de-duplicates by `path` so two callers
asking for the same cache file (e.g. the same URL referenced twice
in a config) can't race on download_content's non-atomic write. When
duplicates are present, the first-seen URL for that path wins.
- Clamp `max_workers` to at least 1 so an invalid caller value can't
raise ValueError out of ThreadPoolExecutor.