feat: retry the restore backup download

Extracts the download body to download_once and makes download_backup a
retry wrapper around it. This path had no retry at all before, so a
single dropped connection failed the whole restore job.

Retrying is safe because File::create truncates and the target filename
is derived from Content-Disposition or the URL, so it is stable across
attempts. There is no Range resume: a download that fails at 90% starts
over.

src/services/restore/downloader.rs

@@ -8,6 +8,7 @@ use std::sync::Arc;
 use std::time::Instant;
 use tokio::io::AsyncWriteExt;
 use crate::services::backup::logger::JobLogger;
+use crate::utils::retry::{RetryPolicy, retry};
 
 fn human_size(bytes: u64) -> String {
     if bytes >= 1024 * 1024 {
@@ -26,6 +27,28 @@ impl RestoreService {
         tmp_path: &Path,
         logger: Arc<JobLogger>,
         expected_size: Option<String>,
+    ) -> Result<PathBuf> {
+        let policy = RetryPolicy::default();
+
+        let logger_ref = &logger;
+
+        retry("Backup download", &logger, &policy, move |_| {
+            let expected = expected_size.clone();
+
+            async move {
+                self.download_once(file_url, tmp_path, Arc::clone(logger_ref), expected)
+                    .await
+            }
+        })
+        .await
+    }
+
+    pub async fn download_once(
+        &self,
+        file_url: &str,
+        tmp_path: &Path,
+        logger: Arc<JobLogger>,
+        expected_size: Option<String>,
     ) -> Result<PathBuf> {
         logger.log("info", "Start downloading backup archive".to_string());
 

src/tests/services/mod.rs

@@ -3,3 +3,4 @@ mod backup_runner_tests;
 mod backup_uploader_tests;
 mod config_tests;
 mod dashboard_config_tests;
+mod restore_downloader_tests;

src/tests/services/restore_downloader_tests.rs

@@ -0,0 +1,64 @@
+use crate::core::context::Context;
+use crate::services::api::ApiClient;
+use crate::services::backup::logger::JobLogger;
+use crate::services::restore::RestoreService;
+use crate::tests::init_tracing_for_test;
+use crate::utils::edge_key::EdgeKey;
+
+use std::sync::Arc;
+use tempfile::TempDir;
+use wiremock::matchers::{method, path};
+use wiremock::{Mock, MockServer, ResponseTemplate};
+
+#[tokio::test]
+async fn a_failing_download_is_retried_until_it_succeeds() {
+    init_tracing_for_test();
+    let server = MockServer::start().await;
+
+    Mock::given(method("GET"))
+        .and(path("/backups/archive.tar.gz"))
+        .respond_with(ResponseTemplate::new(503))
+        .up_to_n_times(2)
+        .with_priority(1)
+        .expect(2)
+        .mount(&server)
+        .await;
+
+    Mock::given(method("GET"))
+        .and(path("/backups/archive.tar.gz"))
+        .respond_with(ResponseTemplate::new(200).set_body_bytes(b"portabase-archive".to_vec()))
+        .with_priority(2)
+        .expect(1)
+        .mount(&server)
+        .await;
+
+    let ctx = Context {
+        edge_key: EdgeKey {
+            server_url: server.uri(),
+            agent_id: "agent-1".to_string(),
+            master_key_b64: String::new(),
+        },
+        api: ApiClient::new(server.uri()),
+    };
+
+    let service = RestoreService::new(Arc::new(ctx));
+
+    let temp_dir = TempDir::new().unwrap();
+    let logger = Arc::new(JobLogger::new());
+    let url = format!("{}/backups/archive.tar.gz", server.uri());
+
+    let downloaded = service
+        .download_backup(&url, temp_dir.path(), Arc::clone(&logger), None)
+        .await
+        .unwrap();
+
+    assert_eq!(std::fs::read(&downloaded).unwrap(), b"portabase-archive");
+
+    let entries = Arc::try_unwrap(logger).unwrap().into_entries();
+    assert_eq!(entries.iter().filter(|e| e.level == "warn").count(), 2);
+    assert!(
+        entries
+            .iter()
+            .any(|e| e.message == "Backup download succeeded on attempt 3/3")
+    );
+}