A page's files are looked up by feed and item, not item alone (#344)

entries_where found a page's enclosures with guid IN (...). The only
index is enclosures_entry (feed_id, guid), so Postgres read the whole
of it: 587k rows, 9,150 buffers and 250 ms for user 2's 50 newest, on
every /api/entries, feed page, Signal page and single item. With the
page's feed ids as well it is an index lookup, 0.5 ms.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ipx/src/db.rs

@@ -1498,8 +1498,12 @@ impl Db {
 
         // Only the guids on this page, so a feed with thousands of entries stays cheap. A page
         // can span feeds, so each file is matched to its row by feed as well as guid, below.
+        // The page's feeds too: the index is (feed_id, guid), and by guid alone Postgres read
+        // all of it, 587k rows and 250 ms for a page of 50 (#344).
+        let feeds: std::collections::BTreeSet<&str> = rows.iter().map(|r| r.feed_id.as_str()).collect();
         let encs = tracing::Instrument::instrument(
             enclosures::Entity::find()
+                .filter(enclosures::Column::FeedId.is_in(feeds.into_iter().map(str::to_owned)))
                 .filter(enclosures::Column::Guid.is_in(rows.iter().map(|r| r.guid.clone())))
                 .order_by_asc(enclosures::Column::Id)
                 .all(&self.orm),