Added a download timestamp

shanty-data/src/mb_import.rs

@@ -589,6 +589,18 @@ pub async fn download_dump(
     let url = format!("{DUMP_BASE_URL}{timestamp}/{filename}");
     let target_path = target_dir.join(filename);
 
+    // Skip if we already have this file from the same dump timestamp
+    let stamp_path = target_dir.join(format!("{filename}.timestamp"));
+    if target_path.exists() {
+        if let Ok(existing_stamp) = std::fs::read_to_string(&stamp_path) {
+            if existing_stamp.trim() == timestamp {
+                progress(&format!("Skipping {filename} (already downloaded from {timestamp})"));
+                tracing::info!(file = %filename, timestamp = %timestamp, "dump file already up to date, skipping download");
+                return Ok(target_path);
+            }
+        }
+    }
+
     progress(&format!("Downloading {filename}..."));
     tracing::info!(url = %url, target = %target_path.display(), "downloading MB dump");
 
@@ -634,6 +646,9 @@ pub async fn download_dump(
         "download complete"
     );
 
+    // Write timestamp marker so we can skip this file on re-runs
+    let _ = std::fs::write(&stamp_path, timestamp);
+
     Ok(target_path)
 }