Apple Podcasts' top charts into the directory weekly, and its categories checked (#252)

With apple_country set, the directory fetches Apple's top 100 podcasts and the top 50 of each of
its 19 categories for that country (itunes.apple.com/{cc}/rss/toppodcasts), looks up each
show's RSS address (/lookup, 100 ids a call, three seconds apart, as Apple asks for no more than
about twenty a minute), and stores them as the snapshot apple-podcasts with no subscribers. The
refresher fetches them like any feed; the most-subscribed chart is unchanged. Apple's primary
genre goes in as the snapshot's category, used only while a feed names none.

The same weekly run reads Apple's genre tree (ws/genres?id=26) and warns when it differs from
ipx_feed's CATEGORIES; on 2026-10-15 they were the same, all 19 and their subcategories.

A syncs table keeps when it last ran: at start if a week has passed, again weekly, an hour after
a failure. keep_instances spares apple-podcasts, which no token holds, and no token may take
the name. A trace a sync, a span each answer.

CLAUDE.md: builds one cargo command at a time, the load looked at before and after, after a
build chained with a test compile took Tower past 200.

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

crates/directory/src/config.rs

@@ -18,6 +18,11 @@ pub struct Config {
     /// publishes: `0.0.0.0:9188`. Empty serves none.
     #[serde(default)]
     pub metrics_bind: String,
+    /// Apple Podcasts' top charts for this country (its two letters: `ca`, `us`) come into the
+    /// directory each week, and Apple's categories are checked against ipx's (#252). Empty, or
+    /// left out, does neither.
+    #[serde(default)]
+    pub apple_country: String,
     #[serde(default)]
     pub tokens: Vec<TokenCfg>,
 }
@@ -81,6 +86,14 @@ impl Config {
             if !seen.insert(t.name.as_str()) {
                 bail!("two tokens are named {:?}", t.name);
             }
+            // Apple's charts are filed under it; a server of that name would replace them.
+            if t.name == crate::apple::INSTANCE {
+                bail!("{:?} is the name Apple Podcasts' charts are kept under; give the token another", t.name);
+            }
+        }
+        let c = cfg.apple_country.trim();
+        if !c.is_empty() && !(c.len() == 2 && c.chars().all(|c| c.is_ascii_alphabetic())) {
+            bail!("apple_country is a country's two letters, such as \"ca\" or \"us\", not {c:?}");
         }
         Ok(cfg)
     }