Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: simongdavies

src/js-host-api/src/lib.rs

@@ -812,7 +812,9 @@ impl JSSandboxWrapper {
     /// Calling `dispose()` on an already-consumed sandbox is a no-op.
     #[napi]
     pub fn dispose(&self) -> napi::Result<()> {
-        let _ = self.inner.lock().map_err(|_| lock_error())?.take();
+        if let Ok(mut guard) = self.inner.lock() {
+            let _ = guard.take();
+        }
         Ok(())
     }
 }
@@ -1174,9 +1176,14 @@ impl LoadedJSSandboxWrapper {
     ///
     /// Calling `dispose()` on an already-consumed sandbox is a no-op.
     #[napi]
-    pub fn dispose(&self) -> napi::Result<()> {
-        let _ = self.inner.lock().map_err(|_| lock_error())?.take();
-        Ok(())
+    pub async fn dispose(&self) -> napi::Result<()> {
+        let inner = self.inner.clone();
+        tokio::task::spawn_blocking(move || {
+            let _ = inner.lock().map_err(|_| lock_error())?.take();
+            Ok(())
+        })
+        .await
+        .map_err(join_error)?
     }
 }