Feeder can delete articles which are present in the feed if articles have disappeared from the middle of the feed

[spacecowboy]

Discussed in #573

^{Originally posted by Garmelon January 31, 2025}
Hello, I follow a custom feed where articles are sometimes deleted while other, older articles remain. When there's more articles than the feed limit, feeder seems to delete older articles that are still present in the feed while keeping newer articles that are no longer present in the feed. This is not ideal since I haven't yet read all the older entries.

One feature that would solve my problem is prioritizing articles in the feed and articles not in the feed differently regarding the feed limit instead of using just the article date. In other words, I'm imagining an algorithm along the lines of

while len(feed) > feed_limit and feed.contains_article_not_in_feed():
    feed.remove_oldest_article_not_in_feed()
while len(feed) > feed_limit:
    feed.remove_oldest_article()

Not sure how difficult this would be to implement as it requires keeping track of which messages were present when the feed was last fetched. It also seems like a niche use case since feeds don't usually change significantly.

On the other hand, one might imagine as a potentially realistic example a feed with more than feed_limit articles that mistakenly publishes and then retracts an article.

PS: I just wanted to mention that this is a very nice and robust app, and I've not encountered any actual issues in quite a while of using it. Thanks for creating it!

Edit: I've split up my feed so this isn't too relevant to me any more.