Get the newest channel or playlist RSS entries

Zero credits. Supply exactly one channel or playlist. Reads only YouTube public RSS, with a ten-minute cache and at most the newest fifteen entries. Allows 500 requests per free key per UTC day or 5,000 per paid key, including valid feed-cache hits. The allowance is checked before upstream work; exhaustion returns 429 QuotaExceeded with Retry-After until 00:00 UTC. The normal key request rate also applies. A UC ID or a channel URL containing that ID works directly; a handle must already be known from channel resolution. Unknown aliases return 400 channel_resolution_required with resolve_url. Latest uploads never calls a relay or the YouTube Data API and never fetches transcripts. This limited feed is not full channel or playlist enumeration. YouTube returned 404 for a well-formed channel or playlist RSS feed ID. Returns nonretryable NotFound with code feed_not_found; check the ID before retrying. Costs zero credits.