Harden Apple Watch snapshot synchronization

crates/watch-apple/src/lib.rs

@@ -185,6 +185,18 @@ impl WatchCore {
             .map_err(Into::into)
     }
 
+    pub fn apply_authoritative_snapshot(
+        &self,
+        snapshot: Vec<u8>,
+    ) -> Result<WatchSnapshotUpdate, WatchFfiError> {
+        self.runtime
+            .lock()
+            .map_err(|_| lock_error())?
+            .apply_authoritative_snapshot(snapshot)
+            .map(Into::into)
+            .map_err(Into::into)
+    }
+
     pub fn presentation_at(&self, unix_seconds: u64) -> Result<WatchPresentation, WatchFfiError> {
         self.runtime
             .lock()