fix: offline download — wait for completion, suppress transient errors

createPack() resolves when the pack is registered, not when tiles are
done downloading. Wrapping in a Promise that resolves only on
status.state === 'complete' keeps the progress modal visible and the
'Download complete' alert fires only when the pack is actually ready.

Transient tile errors ('stream was reset: CANCEL') are silently ignored
in the error listener — MapLibre retries them internally and they do not
indicate a failed download. The onError callback is removed from the
public API since it was causing spurious alerts mid-download.

src/services/offline.ts

@@ -22,31 +22,43 @@ export interface OfflineRegion {
 
 // ── Download ──────────────────────────────────────────────────────────────────
 
-export async function downloadRegion(
+/**
+ * Download a region and return a Promise that resolves only when the pack
+ * reaches state 'complete'. Transient tile-fetch errors (e.g. "stream was
+ * reset: CANCEL") are silently ignored — MapLibre retries them internally
+ * and they do not indicate a failed download.
+ */
+export function downloadRegion(
   name: string,
   bounds: LngLatBounds,
   onProgress: (pct: number, tilesDown: number, sizeBytes: number) => void,
-  onError: (msg: string) => void,
 ): Promise<string> {
   OfflineManager.setProgressEventThrottle(500);
 
-  const pack = await OfflineManager.createPack(
-    {
-      mapStyle: OFFLINE_STYLE_URL,
-      bounds,
-      minZoom: MIN_ZOOM,
-      maxZoom: MAX_ZOOM,
-      metadata: { name, createdAt: new Date().toISOString() },
-    },
-    (_pack, status: OfflinePackStatus) => {
-      onProgress(status.percentage, status.completedTileCount, status.completedTileSize);
-    },
-    (_pack, error) => {
-      onError(error.message);
-    },
-  );
+  return new Promise((resolve, reject) => {
+    let packId: string;
 
-  return pack.id;
+    OfflineManager.createPack(
+      {
+        mapStyle: OFFLINE_STYLE_URL,
+        bounds,
+        minZoom: MIN_ZOOM,
+        maxZoom: MAX_ZOOM,
+        metadata: { name, createdAt: new Date().toISOString() },
+      },
+      (pack, status: OfflinePackStatus) => {
+        packId = pack.id;
+        onProgress(status.percentage, status.completedTileCount, status.completedTileSize);
+        if (status.state === 'complete') {
+          resolve(packId);
+        }
+      },
+      (_pack, _error) => {
+        // Transient tile-level errors — MapLibre retries these automatically.
+        // Do not reject: the overall download is still in progress.
+      },
+    ).catch(reject); // only rejects on createPack failure (e.g. bad style URL)
+  });
 }
 
 // ── List ──────────────────────────────────────────────────────────────────────