ipx-feed's lib.rs splits into leaf modules (#356)

lib.rs held 2,000 lines: fetching, parsing, OPML, Patreon, discovery,
artwork, categories, Jev and redaction, and their tests. It is now the
module list and the re-exports, so ipx and the directory call
feed::fetch, feed::parse and the rest as before:

  fetch.rs      fetch and its limits    parse.rs     RSS and Atom
  outlines.rs   OPML (not opml.rs, which would shadow the opml crate)
  patreon.rs    a creator's shows       discover.rs  finding a feed
  wordpress.rs  WordPress.com's API     failure.rs   failures in words
  privacy.rs    redact, looks_private   artwork.rs   https art, icons
  category.rs   Apple's categories      jev.rs       Jev's category

Moved verbatim, private items pub(crate) where a sibling calls them,
calls across modules module::function. Every definition and doc comment
line of the old lib.rs is in exactly one of the new files; each test
went with what it tests, and all 40 run.

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

crates/feed/src/jev.rs

@@ -0,0 +1,67 @@
+//! Asking TypeSafe's Jev which Apple category a feed belongs to.
+
+use crate::parse::ParsedFeed;
+use crate::{category, fetch};
+use anyhow::{Result, anyhow};
+
+/// TypeSafe's System One endpoint, where Jev answers questions about a piece of state.
+pub const JEV_URL: &str = "https://api.typesafe.ai/v1/systemone";
+
+/// A Directory category for a feed that names none of its own, which most blogs do not (#117):
+/// TypeSafe's Jev picks one of Apple's categories or subcategories from the feed's title and
+/// latest items, the subcategory being what a podcast's own category is stored as. The likeliest
+/// is taken however unsure, since an admin can change it and asking again would cost a call a scan.
+pub async fn classify(client: &reqwest::Client, key: &str, feed: &ParsedFeed) -> Result<String> {
+    let items: Vec<&str> = feed.entries.iter().filter_map(|e| e.title.as_deref()).take(15).collect();
+    // A subcategory says which category it is in; without that, "Games" or "Drama" is ambiguous.
+    let mut criteria = serde_json::Map::new();
+    for (category, subs) in category::CATEGORIES {
+        criteria.insert(category.to_string(), serde_json::Value::Null);
+        for sub in *subs {
+            criteria.insert(sub.to_string(), format!("Within {category}").into());
+        }
+    }
+    let body = serde_json::json!({
+        "model": "jev-latest",
+        "state": { "title": feed.title, "recent_items": items },
+        "questions": { "category": {
+            "type": "choice",
+            "instructions": "Which category best describes what this feed publishes?",
+            "criteria": criteria,
+        }},
+    });
+    let answer: serde_json::Value = client
+        .post(JEV_URL)
+        .bearer_auth(key)
+        .json(&body)
+        .timeout(fetch::FEED_TIMEOUT)
+        .send()
+        .await?
+        .error_for_status()?
+        .json()
+        .await?;
+    picked(&answer)
+}
+
+pub(crate) fn picked(answer: &serde_json::Value) -> Result<String> {
+    let choice = answer["answers"]["category"]["choice"].as_str().unwrap_or_default();
+    category::CATEGORIES
+        .iter()
+        .flat_map(|(c, subs)| std::iter::once(c).chain(subs.iter()))
+        .find(|c| **c == choice)
+        .map(|c| c.to_string())
+        .ok_or_else(|| anyhow!("no category in the answer: {answer}"))
+}
+
+#[cfg(test)]
+mod tests {
+
+    #[test]
+    fn picked_takes_only_an_apple_category() {
+        let answer = |c: &str| serde_json::json!({"answers": {"category": {"type": "choice", "choice": c}}});
+        assert_eq!(super::picked(&answer("Technology")).unwrap(), "Technology");
+        assert_eq!(super::picked(&answer("Tech News")).unwrap(), "Tech News", "a subcategory");
+        assert!(super::picked(&answer("Blogs")).is_err(), "not one of Apple's");
+        assert!(super::picked(&serde_json::json!({"error": "rate limited"})).is_err());
+    }
+}