fix(ui): don't strand the Mini App on a cancelled GCG share

On iOS WKWebView (the Telegram Mini App), cancelling the Web Share sheet fell
through to the Blob <a download> fallback. iOS ignores the download attribute,
so clicking the anchor navigated the webview to the blob: URL — replacing the
SPA with the raw GCG file, with no way back (force-quit only).

The share path no longer falls back to a download: Web Share is available on
that platform, so a cancelled or failed share is a no-op and the user can
retry. The Blob download stays the desktop-only path (no Web Share).

ui/src/lib/share.test.ts

@@ -1,8 +1,11 @@
-import { describe, expect, it } from 'vitest';
+import { afterEach, describe, expect, it, vi } from 'vitest';
-import { pickGcgDelivery } from './share';
+import { pickGcgDelivery, shareOrDownloadGcg } from './share';
+import type { GcgExport } from './model';
 
 const file = {} as File;
 
+const gcg: GcgExport = { gameId: 'g1', filename: 'game.gcg', content: '#title game' };
+
 describe('pickGcgDelivery', () => {
   it('shares when the platform can share files', () => {
     expect(pickGcgDelivery({ canShare: () => true, share: async () => {} }, file)).toBe('share');
@@ -20,3 +23,40 @@ describe('pickGcgDelivery', () => {
     expect(pickGcgDelivery({ canShare: () => true } as never, file)).toBe('download');
   });
 });
+
+describe('shareOrDownloadGcg', () => {
+  afterEach(() => vi.unstubAllGlobals());
+
+  function stubDownloadEnv(canShare: boolean, share: () => Promise<void>) {
+    const anchor = { href: '', download: '', click: vi.fn(), remove: vi.fn() };
+    const createElement = vi.fn(() => anchor);
+    vi.stubGlobal('File', class {});
+    vi.stubGlobal('Blob', class {});
+    vi.stubGlobal('navigator', { canShare: () => canShare, share });
+    vi.stubGlobal('document', { createElement, body: { appendChild: vi.fn() } });
+    vi.stubGlobal('URL', { createObjectURL: vi.fn(() => 'blob:x'), revokeObjectURL: vi.fn() });
+    return { anchor, createElement };
+  }
+
+  it('never falls back to the navigating Blob download when a share is cancelled', async () => {
+    // Reproduces the iOS Telegram Mini App break: Web Share is available and the user cancels it
+    // (AbortError). The <a download> fallback navigates the WKWebView to the blob: URL and strands
+    // the app, so a cancelled (or failed) share must do nothing here.
+    const share = vi.fn().mockRejectedValue(new DOMException('cancelled', 'AbortError'));
+    const { createElement } = stubDownloadEnv(true, share);
+
+    await shareOrDownloadGcg(gcg);
+
+    expect(share).toHaveBeenCalledOnce();
+    expect(createElement).not.toHaveBeenCalled(); // no download anchor → no webview navigation
+  });
+
+  it('downloads via an anchor when the platform cannot share files', async () => {
+    const { anchor, createElement } = stubDownloadEnv(false, vi.fn());
+
+    await shareOrDownloadGcg(gcg);
+
+    expect(createElement).toHaveBeenCalledWith('a');
+    expect(anchor.click).toHaveBeenCalledOnce();
+  });
+});

ui/src/lib/share.ts

@@ -25,12 +25,17 @@ export async function shareOrDownloadGcg(gcg: GcgExport): Promise<void> {
   const file = new File([gcg.content], gcg.filename, { type: 'application/x-gcg' });
   const nav = typeof navigator !== 'undefined' ? navigator : undefined;
   if (pickGcgDelivery(nav, file) === 'share' && nav) {
+    // Web Share is available (mobile, including the iOS Telegram Mini App): use it and stop here
+    // whatever the outcome. Do NOT fall back to the Blob download — on iOS WKWebView an
+    // <a download> navigates the webview to the blob: URL, replacing the SPA with the raw file
+    // and stranding the app, so a cancelled or failed share must simply do nothing (the user can
+    // retry). The download path is only for desktop browsers without Web Share.
     try {
       await nav.share({ files: [file], title: gcg.filename });
-      return;
     } catch {
-      // The user cancelled or sharing failed — fall back to a download.
+      /* cancelled or failed — intentionally a no-op (see above) */
     }
+    return;
   }
   downloadFile(gcg.content, gcg.filename);
 }