Feed hosted on GitHub infra only persists 4 entries (document order); nginx feeds fine

Bug: Every feed hosted on GitHub infra only persists 4 entries; nginx-hosted feeds work fine

Platform: macOS Desktop (also reproduced on folo.is web, same account)

Describe the bug

For feeds hosted on GitHub infrastructure (GitHub Pages, raw.githubusercontent.com, gist.githubusercontent.com), a newly subscribed feed only ever shows exactly 4 entries — specifically the first 4 <item> elements in document order — regardless of feed content, size, item count, or XML structure. A control feed hosted on plain nginx (news.ycombinator.com/rss) shows all ~30 entries normally.

Repro feeds (all show 4 entries):

URL	item count	notes
https://xlicz.github.io/podcast-rss/feed.xml	176	Chinese content, 1.9MB, content:encoded full text
https://xlicz.github.io/podcast-rss/feed-lite.xml	176	no content:encoded, 76KB, date-desc
https://xlicz.github.io/podcast-rss/feed-mini.xml	50	no content:encoded, 24KB
https://xlicz.github.io/podcast-rss/feed-t3-ascii.xml	20	100% ASCII, standard channel, +0000 dates, 5.5KB
https://xlicz.github.io/podcast-rss/feed-t4-times.xml	20	ASCII, distinct per-item timestamps
https://xlicz.github.io/podcast-rss/feed-t7-three.xml	3	still shows 4
https://gist.githubusercontent.com/xlicz/47d26652fdab176723ac95fbb5306987/raw/feed-t3-ascii.xml	20	same bytes as t3, gist origin
https://raw.githubusercontent.com/xlicz/podcast-rss/main/feed.xml	176	raw origin

Eliminated hypotheses (each tested with a dedicated feed variant):

• feed size / partial transfer (24KB mini feed also shows 4; cold Pages fetch measured 1.1-1.4s total)
• robots.txt (deleted site robots.txt, still 4)
• content:encoded full-text HTML (stripped in lite/mini)
• single-line serialization (pretty-printed variants)
• guid isPermaLink="false" (removed in t2)
• non-ASCII titles/links (t3 is 100% ASCII)
• identical pubDates (t4 has distinct timestamps)
• channel meta order / language element / lastBuildDate (rebuilt channels)
• XML declaration style

Control that works: https://news.ycombinator.com/rss (nginx, ASCII, +0000) — shows all ~30 entries in the same account.

Key observation: the 4 displayed entries are always the first 4 in document order. A 3-item feed (t7) still displays 4. All failing feeds share: (a) GitHub CDN hosting, (b) same channel <link> value https://xlicz.github.io/podcast-rss.

Could this be related to GitHub-family URL detection (github.io / githubusercontent) in the server's fetch pipeline, or an entry-store preview limit where the async full-fetch job fails only for GitHub-hosted URLs?

Any server-side guidance (or a way to see why the async fetch fails) would be appreciated — the feeds themselves parse fine with ElementTree, feedparser, and r.jina.ai's reader.