fix(ios): bind export cancellation to the originating download

Ignore late picker callbacks that no longer match the active download. Add an Apple-platform regression; Swift formatting, parsing and seven portable policy tests pass locally, but the new WKWebView regression requires Xcode and has not run here.

ios/Sources/BrowserModel.swift

@@ -103,7 +103,8 @@ final class BrowserModel: NSObject, ObservableObject, WKNavigationDelegate, WKUI
         authentication = WebDestination(url: url)
     }
 
-    func removeDownload() {
+    func removeDownload(expected: URL? = nil) {
+        if let expected, download?.url != expected, downloadLocation != expected { return }
         download = nil
         if let location = downloadLocation {
             try? FileManager.default.removeItem(at: location.deletingLastPathComponent())