release(v1.7.15-alpha): bulletproof downloads — resume, retry, real progress

download_update
  Each component download is now resumable via HTTP Range requests
  (Range: bytes=N-) and retried up to 6 times with exponential
  backoff (5/15/30/60/120/180s). On a dropped connection the next
  attempt picks up at the last written byte offset instead of
  restarting at zero. Streams via reqwest::Response::chunk() to the
  staging file so a 160 MB frontend tarball doesn't sit in RAM. SHA
  is verified over the complete file at the end of each component;
  mismatch nukes the staged file and restarts from scratch.

Real download progress counters
  New AtomicU64 globals DOWNLOAD_BYTES/DOWNLOAD_TOTAL are updated
  from the chunk loop. update.status exposes them as
  download_progress.{bytes_downloaded, total_bytes, active}. The
  SystemUpdate.vue progress bar now polls update.status every
  second instead of incrementing a fake random counter — and
  crucially, if the user navigates away and back, the component
  picks up the in-progress download from the backend atomics
  immediately.

Update-check retries
  handle_update_check now retries the manifest fetch up to 3 times
  with a 5s gap if the first try hits a transport error, so a
  momentary gitea hiccup doesn't make a node report "up to date"
  when there actually is a new release. Tight 10s connect timeout
  per attempt keeps the total bounded.

Artefacts:
  archipelago                                      1070c87f…c081c162b  40584792
  archipelago-frontend-1.7.15-alpha.tar.gz         8e630eba…63fd43f   162078068

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

core/archipelago/src/api/rpc/update.rs

@@ -157,6 +157,16 @@ impl RpcHandler {
     /// Get update status without checking remote.
     pub(super) async fn handle_update_status(&self) -> Result<serde_json::Value> {
         let state = update::get_status(&self.config.data_dir).await?;
+        // Expose live download progress so the UI can resume the
+        // progress bar after navigation instead of showing the fake
+        // creep again. An RPC poll every ~1s during download drives a
+        // real progress indicator that survives route changes.
+        let downloaded = update::DOWNLOAD_BYTES
+            .load(std::sync::atomic::Ordering::Relaxed);
+        let total = update::DOWNLOAD_TOTAL
+            .load(std::sync::atomic::Ordering::Relaxed);
+        let active = total > 0 && downloaded < total;
+        let completed = total > 0 && downloaded >= total;
 
         Ok(serde_json::json!({
             "current_version": state.current_version,
@@ -164,6 +174,13 @@ impl RpcHandler {
             "update_available": state.available_update.is_some(),
             "update_in_progress": state.update_in_progress,
             "rollback_available": state.rollback_available,
+            "download_progress": if active || completed {
+                Some(serde_json::json!({
+                    "bytes_downloaded": downloaded,
+                    "total_bytes": total,
+                    "active": active,
+                }))
+            } else { None },
         }))
     }