fix(retry): honor attempt caps per download URL

src-tauri/src/download.rs

@@ -429,9 +429,12 @@ async fn download_file(
     // The legacy `max_tries` payload field is still honored as a cap on
     // attempts, but transient backoff is additionally bounded by
     // `retry::MAX_RETRIES` so a single URL cannot spin forever.
-    let mut strike = 0_usize;
+    let max_attempts = payload.max_tries.max(1) as usize;
     'url: for url in &payload.urls {
+        let mut strike = 0_usize;
+        let mut attempts = 0_usize;
         loop {
+            attempts += 1;
             match download_attempt(&events, &client, &payload, url, &mut control_rx).await {
                 Ok(()) => return DownloadOutcome::Completed,
                 Err(AttemptError::Controlled(DownloadControl::Pause)) => {
@@ -446,34 +449,45 @@ async fn download_file(
                 }
                 Err(AttemptError::Failed(error)) => {
                     last_error = error.clone();
-                    let transient = crate::retry::is_transient_network_error(&error);
-                    let strikes_left = strike < crate::retry::MAX_RETRIES;
-                    if !(transient && strikes_left) {
-                        // Permanent error (e.g. HTTP 404 / disk full) or the
-                        // 3-strike budget is exhausted — advance to the next URL.
-                        strike = 0;
+
+                    if attempts >= max_attempts {
                         continue 'url;
                     }
 
-                    // Transient: announce `Retrying`, back off, then retry.
-                    // The backoff sleep is itself cancelable so a user
-                    // pause/cancel during the wait is honored immediately.
-                    events.emit_retrying(payload.id, strike, error);
-                    let delay = crate::retry::backoff_for(strike);
-                    tokio::select! {
-                        _ = tokio::time::sleep(delay) => {}
-                        control = control_rx.recv() => {
-                            return match control.unwrap_or(DownloadControl::Cancel) {
-                                DownloadControl::Pause => DownloadOutcome::Paused,
-                                DownloadControl::Cancel => {
-                                    let _ = fs::remove_file(&payload.output_path).await;
-                                    DownloadOutcome::Cancelled
-                                }
-                                DownloadControl::Replace => DownloadOutcome::Cancelled,
-                            };
+                    let transient = crate::retry::is_transient_network_error(&error);
+                    let strikes_left = strike < crate::retry::MAX_RETRIES;
+
+                    if transient && strikes_left {
+                        // Transient: announce `Retrying`, back off, then retry.
+                        // The backoff sleep is itself cancelable so a user
+                        // pause/cancel during the wait is honored immediately.
+                        events.emit_retrying(payload.id, strike, error);
+                        let delay = crate::retry::backoff_for(strike);
+                        tokio::select! {
+                            _ = tokio::time::sleep(delay) => {}
+                            control = control_rx.recv() => {
+                                return match control.unwrap_or(DownloadControl::Cancel) {
+                                    DownloadControl::Pause => DownloadOutcome::Paused,
+                                    DownloadControl::Cancel => {
+                                        let _ = fs::remove_file(&payload.output_path).await;
+                                        DownloadOutcome::Cancelled
+                                    }
+                                    DownloadControl::Replace => DownloadOutcome::Cancelled,
+                                };
+                            }
                         }
+                        strike += 1;
+                        continue;
                     }
-                    strike += 1;
+
+                    if !transient && !crate::retry::is_permanent_network_error(&error) {
+                        // Legacy `max_tries` cap for ambiguous HTTP statuses (e.g.
+                        // 500) that are neither clearly transient nor permanent.
+                        continue;
+                    }
+
+                    // Permanent error or transient strike budget exhausted.
+                    continue 'url;
                 }
             }
         }

src-tauri/src/retry.rs

@@ -72,12 +72,8 @@ pub fn backoff_for(strike: usize) -> Duration {
 /// 401/403/404/410/451, "not found", permission denied, out-of-disk. The
 /// permanent list is checked first so a composite message (e.g. an HTTP 404
 /// that also mentions "timeout" in a URL) still fails fast.
-pub fn is_transient_network_error(message: &str) -> bool {
+pub fn is_permanent_network_error(message: &str) -> bool {
     let m = message.to_ascii_lowercase();
-
-    // Permanent conditions win — never retry a 404/403/410/401/451, a missing
-    // file, a permission error, or a full disk, even if the message also
-    // contains a transient keyword (e.g. "timeout" inside a URL path).
     const PERMANENT: [&str; 9] = [
         "http 401",
         "http 403",
@@ -89,11 +85,17 @@ pub fn is_transient_network_error(message: &str) -> bool {
         "permission denied",
         "no space left on device",
     ];
-    if PERMANENT.iter().any(|p| m.contains(p)) {
+    PERMANENT.iter().any(|p| m.contains(p))
+}
+
+pub fn is_transient_network_error(message: &str) -> bool {
+    if is_permanent_network_error(message) {
         return false;
     }
 
-    const TRANSIENT: [&str; 18] = [
+    let m = message.to_ascii_lowercase();
+
+    const TRANSIENT: [&str; 20] = [
         // reqwest / hyper / OS socket-layer
         "timed out",
         "timeout",
@@ -112,6 +114,8 @@ pub fn is_transient_network_error(message: &str) -> bool {
         // HTTP-level transient
         "http 408",
         "request timeout",
+        "http 503",
+        "503 service unavailable",
         // aria2c log phrasing
         "connection was closed",
         "timeout.",
@@ -204,6 +208,14 @@ mod tests {
         assert!(is_transient_network_error("request timeout"));
     }
 
+    #[test]
+    fn classifies_http_503_as_transient() {
+        assert!(is_transient_network_error("HTTP 503 Service Unavailable"));
+        assert!(is_transient_network_error(
+            "http://127.0.0.1/file returned HTTP 503 Service Unavailable"
+        ));
+    }
+
     #[test]
     fn classifies_ytdlp_and_aria2_phrasing_as_transient() {
         assert!(is_transient_network_error(