I finally sat down today to diagnose the problem and discovered I was missing a record from the serendipity_permalinks table which was stopping s9y from being able to look up the id of the category. It was my craft category which is id 7 - all I had to do was run the following against mysql:
insert into serendipity_permalinks set permalink = "category/craft", entry_id=7, type="category";
So now my craft category works fine. If anyone knows how to stop my feeds from showing old articles as new when I edit them but don't update the publication date, I'd be grateful! A bunch of imported posts are still missing their images, would be nice to be able to fix these without polluting my feed.
I edited an old post, because the image links were broken (I did have a nightmare migrating because I was so inconsistent about the format of the image tags in textpattern, completely my own fault). I was very careful not to update the published date of the article, however the edited article appeared in the feed, which wasn't what I had in mind! It turned out that this is by design. On line 262 of includes/functions_entries.inc.php (I have serendipity 1.1.3), I found this:
$cond['orderby'] = 'last_modified DESC';
I've commented out this line, which was in an if($modified_since) clause. Hopefully this will stop updated entries from appearing in the feed - I have a few other old ones to fix images in so we'll soon see.
At around the same time, Ivo mentioned that he was seeing the order of posts change in his reader (google reader) when people commented on my posts. I suspect that this is part of the same issue and I'm optimistic of it also being fixed by this change. However when I was looking into the problem I noticed that the URL he was using to access my feed, http://lornajane.net/index.rss2, actually returned RSS 0.91. Not ideal! The problem is the rewrite rule in serendipity's .htaccess file, which looks like this:
RewriteRule ^(index|atom[0-9]*|rss|b2rss|b2rdf).(rss|rdf|rss2|xml) rss.php?file=$1&ext=$2
When you request index.rss2 it should rewrite to rss.php?file=$1&ext=$2 but the "rss" matches first so the user gets redirected to index.rss instead. As a nasty hack to get around this I removed the rss from the above example and gave it a line of its own:
RewriteRule ^(index|atom[0-9]*|rss|b2rss|b2rdf).(rdf|rss2|xml) rss.php?file=$1&ext=$2 RewriteRule ^(index|atom[0-9]*|rss|b2rss|b2rdf).(rss) rss.php?file=$1&ext=rss
Requests to index.rss2 are now correctly rewritten as rss.php?file=index&ext=rss2 and will get RSS 2.0 format in the response. I have just noticed however that this is the most requested page on the site so I really hope I didn't break anything!