Harden Apple Watch snapshot synchronization

apple/Sources/App/IronStorageApp.swift

@@ -46,6 +46,7 @@ private final class WatchSnapshotCoordinator: NSObject, WCSessionDelegate {
             Notification.Name.ironStorageWatchSnapshotDidChange,
             .ironStorageLocalStoreDidChange,
             .ironStorageAuthenticationDidChange,
+            UIApplication.didBecomeActiveNotification,
         ] {
             NotificationCenter.default.addObserver(
                 self,
@@ -103,21 +104,7 @@ private final class WatchSnapshotCoordinator: NSObject, WCSessionDelegate {
                     Self.snapshotKey: snapshot,
                     Self.deliveredReceiptKey: Data(transfer.deliveredReceipt),
                 ]
-                do {
-                    try session.updateApplicationContext(payload)
-                    if session.isReachable {
-                        session.sendMessage(payload, replyHandler: nil) { _ in
-                            session.transferUserInfo(payload)
-                        }
-                    } else {
-                        session.transferUserInfo(payload)
-                    }
-                } catch {
-                    _ = try? authentication.failWatchSnapshot(
-                        revision: transfer.revision,
-                        detail: "The latest Apple Watch snapshot could not be queued."
-                    )
-                }
+                publish(payload, through: session)
                 notifyStatusChanged()
             case .failure:
                 // A locked GPG key leaves the previous replacement pending. Authentication
@@ -127,6 +114,18 @@ private final class WatchSnapshotCoordinator: NSObject, WCSessionDelegate {
         }
     }
 
+    private func publish(_ payload: [String: Any], through session: WCSession) {
+        for transfer in session.outstandingUserInfoTransfers
+        where transfer.userInfo[Self.snapshotKey] != nil {
+            transfer.cancel()
+        }
+        try? session.updateApplicationContext(payload)
+        session.transferUserInfo(payload)
+        if session.isReachable {
+            session.sendMessage(payload, replyHandler: nil) { _ in }
+        }
+    }
+
     private func recordUnavailable(unpaired: Bool, detail: String) {
         guard let authentication else { return }
         _ = try? authentication.setWatchSnapshotUnavailable(unpaired: unpaired, detail: detail)