refactor(site): move cache_key/is_retryable/media_headers into site modules

crates/x-media/src/site/twitter/interface.rs

@@ -49,6 +49,26 @@ pub async fn fetch_from_url(url: &str) -> Result<Fetched, FetchError> {
     }
 }
 
+/// Cache key for a twitter URL: `"twitter:<id>"`. The prefix is the site id
+/// used for caption-format lookup and link-cache keys.
+pub fn cache_key(url: &str) -> Option<String> {
+    PATTERN
+        .captures(url)
+        .map(|caps| format!("twitter:{}", &caps[1]))
+}
+
+/// Twitter's fetch-retry policy: transient classes only. Not-found, blocked,
+/// sensitive (NSFW withholding) and parse failures are permanent — retrying
+/// them only wastes attempts against the syndication endpoint.
+pub fn is_retryable(err: &FetchError) -> bool {
+    matches!(err, FetchError::Http(_) | FetchError::Transient(_))
+}
+
+/// twimg URLs need no extra headers (no hotlink protection).
+pub fn media_headers(_url: &str) -> Option<Vec<(&'static str, String)>> {
+    None
+}
+
 /// A Fetched with no media for withheld tweets: the bot replies
 /// "No media found" and moves on instead of erroring.
 fn empty_fetched(url: &str) -> Fetched {
@@ -354,6 +374,29 @@ mod tests {
         }
     }
 
+    #[test]
+    fn cache_key_prefixes_tweet_id() {
+        assert_eq!(
+            cache_key("https://x.com/user/status/1234567890"),
+            Some("twitter:1234567890".into())
+        );
+        assert_eq!(cache_key("https://example.com/1"), None);
+    }
+
+    #[test]
+    fn is_retryable_classifies_transient_and_permanent() {
+        // Transient: network errors and explicit transient statuses (the
+        // `Http` arm shares this match arm with `Transient`).
+        assert!(is_retryable(&FetchError::Transient("429".into())));
+        // Permanent: gone, blocked, withheld, oversized, unparseable.
+        assert!(!is_retryable(&FetchError::NotFound));
+        assert!(!is_retryable(&FetchError::Blocked));
+        assert!(!is_retryable(&FetchError::Sensitive));
+        assert!(!is_retryable(&FetchError::TooLarge));
+        let json_err = serde_json::from_str::<serde_json::Value>("x").unwrap_err();
+        assert!(!is_retryable(&FetchError::Json(json_err)));
+    }
+
     #[test]
     fn syndication_json_converts_to_fetched() {
         let raw = fixture(serde_json::json!([

crates/x-media/src/site/twitter/mod.rs

@@ -2,4 +2,6 @@ mod auth;
 mod interface;
 mod model;
 
-pub use interface::{PATTERN, Tweet, enabled, fetch_from_url};
+pub use interface::{
+    PATTERN, Tweet, cache_key, enabled, fetch_from_url, is_retryable, media_headers,
+};