perf: retry the bsky HLS request, not the whole fetch

A failed bsky video remux was reported as `FetchError::Transient`, so the
fetch loop retried the *whole* adapter — master playlist, variant playlist
and up to 500 segments again (256 MiB of cap each time), for a failure that
happened near the end of the work the retry was about to redo. The message
had to stay honest (returning `Ok` with no media reads as "this post has no
media"), so it needed a class of its own.

`FetchError::MediaPrep` is that class: post fetched, media could not be
prepared locally, not retryable (the per-site `is_retryable` whitelist
excludes it by construction), with its own user-facing text — the generic
"failed to fetch" would have hidden that the download or encode was what
broke. The retry itself is not lost, it moved: `fetch_hls` retries the
request that actually failed, once, for the classes a retry can change
(transport, 429/5xx).

Checked the sibling sites before widening the change: pixiv already degrades
to no media when the ugoira encode fails (`Ok(None)`), and its frame-zip
download failure is the last step so a re-fetch re-does only that; twitter's
auth leg replays two cheap metadata GETs and a GraphQL 5xx *is* worth
retrying. Neither needed the new class.

Verified with a throwaway proxy harness: a 503 answered twice-in-a-row path
costs 2 requests and succeeds, a 404 costs exactly 1 and fails (no pointless
retry). `site::bsky::interface::tests::media_prep_failure_is_not_retried`
pins the classification.

`cargo fmt --check`, `cargo clippy --workspace --all-targets --locked -- -D
warnings` and `cargo test --workspace --locked` clean.

AGENTS.md

@@ -66,7 +66,7 @@ Docker: `docker build -t tgxmb .` then `docker run --rm -d --name tgxmb --env-fi
 
 ## Code Conventions & Common Patterns
 
-- **Errors via `thiserror` derive** (no anyhow): the public, stringified errors — `FetchError` (`Http`/`Json`/`Pixiv`/`Site`/`NotFound`/`Blocked`/`Disabled`/`Sensitive`/`TooLarge`/`Transient`/`Io`) and `PixivError` — derive `thiserror::Error` with `#[from]` conversions; `Display`/`source()` come from the derive. The internal control-flow enums — `QueueError` (`Retryable { delay_seconds, payload }` / `Permanent`), `SendError` (Retryable/Permanent), `Classification`, `FallbackError` — carry no `Display` and are handled by direct variant matching. New errors should follow the same split: stringified/public errors derive `thiserror`, internal flow enums stay plain.
+- **Errors via `thiserror` derive** (no anyhow): the public, stringified errors — `FetchError` (`Http`/`Json`/`Pixiv`/`Site`/`NotFound`/`Blocked`/`Disabled`/`Sensitive`/`TooLarge`/`MediaPrep`/`Transient`/`Io`) and `PixivError` — derive `thiserror::Error` with `#[from]` conversions; `Display`/`source()` come from the derive. The internal control-flow enums — `QueueError` (`Retryable { delay_seconds, payload }` / `Permanent`), `SendError` (Retryable/Permanent), `Classification`, `FallbackError` — carry no `Display` and are handled by direct variant matching. New errors should follow the same split: stringified/public errors derive `thiserror`, internal flow enums stay plain.
 - **Global state via `std::sync::LazyLock` statics**, not DI: `CONFIG`, `CHAT_STORE`, `TASK_QUEUE` in `handlers/statics.rs`; shared reqwest `CLIENT` in `x-media/src/site/mod.rs`. `Bot` is passed/cloned into handlers; queue workers share the process-wide `send::BOT` (`LazyLock<Bot>`, force-initialized in `main` so a missing token fails at startup).
 - **Async**: tokio multi-thread runtime (`#[tokio::main]` default). All rusqlite I/O inside `tokio::task::spawn_blocking`. Long loops use `tokio::select!` with `tokio::sync::{watch, Notify}` stop/wake channels. No streams.
 - **Blocking sync primitives**: `parking_lot::Mutex` for hot caches, `tokio::sync::Mutex` for async-shared state (pixiv token cache), `AtomicBool` for feature gates.

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

@@ -56,8 +56,11 @@ pub async fn fetch_from_url(url: &str) -> Result<Fetched, FetchError> {
     // `warn` is a level operators share.
     let key = cache_key(url).unwrap_or_else(|| "?".into());
     // A failed remux is remembered: if it leaves the post with no media at
-    // all, returning `Ok` would read as "this post has no media" and skip the
+    // all, returning `Ok` would read as "this post has no media". It is
-    // retry that a transient segment-download failure deserves.
+    // reported as `FetchError::MediaPrep` rather than a transient failure —
+    // the download legs already got their own retry in place ([`fetch_hls`]),
+    // and the fetch loop's retry would only download every segment again to
+    // fail the same way.
     let mut remux_failure: Option<String> = None;
     for item in fetched.media {
         let is_hls = matches!(&item, Media::Video { url, .. }
@@ -93,7 +96,7 @@ pub async fn fetch_from_url(url: &str) -> Result<Fetched, FetchError> {
     if media.is_empty()
         && let Some(reason) = remux_failure
     {
-        return Err(FetchError::Transient(format!(
+        return Err(FetchError::MediaPrep(format!(
             "bsky video remux failed: {reason}"
         )));
     }
@@ -120,6 +123,24 @@ pub fn media_headers(_url: &str) -> Option<Vec<(&'static str, String)>> {
     None
 }
 
+/// One HLS fetch (a playlist or a segment) with an in-place retry for a
+/// retryable class (transport, 429/5xx). These used to get their retry from the
+/// outer fetch loop, which pays for it by replaying the whole post: master
+/// playlist, variant playlist and every segment again. A segment failing near
+/// the end of a 500-segment video meant downloading the entire thing twice
+/// more, so the second attempt belongs on the request that actually failed.
+async fn fetch_hls(url: &str, cap: u64) -> Result<bytes::Bytes, String> {
+    match crate::site::download_media_limited(url, cap).await {
+        Err(FetchError::Http(_) | FetchError::Transient(_)) => {
+            tokio::time::sleep(std::time::Duration::from_secs(1)).await;
+            crate::site::download_media_limited(url, cap)
+                .await
+                .map_err(|e| e.to_string())
+        }
+        other => other.map_err(|e| e.to_string()),
+    }
+}
+
 /// Downloads an HLS playlist (master or media) and remuxes its segments to a
 /// single MP4 via ffmpeg. Returns the MP4 path plus the temp dir that must
 /// stay alive until the file is uploaded. `Ok(None)` when ffmpeg is missing.
@@ -135,7 +156,7 @@ async fn resolve_bsky_video(
         crate::site::log_once_ffmpeg_missing();
         return Ok(None);
     }
-    let master = crate::site::download_media_limited(playlist_url, 1_048_576)
+    let master = fetch_hls(playlist_url, 1_048_576)
         .await
         .map_err(|e| format!("bsky video master playlist: {e}"))?;
     let master = String::from_utf8_lossy(&master);
@@ -170,7 +191,7 @@ async fn resolve_bsky_video(
         playlist_url.to_string()
     };
 
-    let variant = crate::site::download_media_limited(&playlist_url, 1_048_576)
+    let variant = fetch_hls(&playlist_url, 1_048_576)
         .await
         .map_err(|e| format!("bsky video media playlist: {e}"))?;
     let variant = String::from_utf8_lossy(&variant);
@@ -201,7 +222,7 @@ async fn resolve_bsky_video(
     let mut total: u64 = 0;
     let mut list = String::new();
     for (i, seg) in segments.iter().enumerate() {
-        let bytes = crate::site::download_media_limited(seg, 20 * 1024 * 1024)
+        let bytes = fetch_hls(seg, 20 * 1024 * 1024)
             .await
             .map_err(|e| format!("bsky segment {i}: {e}"))?;
         total += bytes.len() as u64;
@@ -422,6 +443,18 @@ mod tests {
         }
     }
 
+    /// A remux failure is a `MediaPrep`, which the fetch loop does not retry:
+    /// replaying the post means downloading every HLS segment again, when the
+    /// request that failed already got its second attempt in place
+    /// ([`fetch_hls`]). The classes below are the ones still retried there.
+    #[test]
+    fn media_prep_failure_is_not_retried() {
+        assert!(!is_retryable(&FetchError::MediaPrep(
+            "bsky video remux failed: segment 400: 503".into()
+        )));
+        assert!(is_retryable(&FetchError::Transient("429".into())));
+    }
+
     #[test]
     fn from_json_images_with_missing_defaults() {
         let raw = thread_json(serde_json::json!({

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

@@ -260,6 +260,13 @@ pub enum FetchError {
     /// A download exceeded the caller's size cap (see [`download_media_limited`]).
     #[error("media too large")]
     TooLarge,
+    /// The post was fetched, but its media could not be prepared locally — a
+    /// download or encode step that runs *after* the site's own response
+    /// (bsky's HLS remux, say). Deliberately not retryable: the retry would
+    /// replay the whole fetch, redoing the download work that just failed
+    /// instead of the request that failed.
+    #[error("media could not be prepared: {0}")]
+    MediaPrep(String),
     /// A transient server-side failure (429 / 5xx); [`fetch`] retries these.
     #[error("transient: {0}")]
     Transient(String),

crates/xmedia-bot/src/handlers/urls.rs

@@ -459,6 +459,11 @@ fn fetch_error_message(err: &x_media::site::FetchError) -> String {
         FetchError::Transient(_) | FetchError::Http(_) => {
             "The source site is unavailable right now (tried 3 times). Try again later.".to_string()
         }
+        FetchError::MediaPrep(_) => concat!(
+            "Could not prepare this post's media (its download or encode failed). ",
+            "Try again later."
+        )
+        .to_string(),
         // Parse/shape surprises, pixiv auth details, oversized media: nothing
         // actionable for the user beyond "this did not work".
         _ => "Failed to fetch media from this link.".to_string(),