Fixes#20525, (thanks @oxura !)
```sh
# Many files that route to the Prettier `formatFile` callback and fail to parse
mkdir -p /tmp/repro
for i in $(seq 1 500); do printf '<template><div></template>' > /tmp/repro/broken$i.vue; done
# Run repeatedly with default concurrency
for run in $(seq 1 10); do node apps/oxfmt/dist/cli.js --write /tmp/repro; done
```
Within a few runs it crashes non-deterministically (exit codes varied: 133 / 138 / 139, and sometimes 2 = clean error report), with the same fatal as #20525:
```
# Fatal error in , line 0
# Check failed: object_ != kGlobalHandleZapValue. (or: node->IsInUse())
...
napi_reference_unref
<napi::error::Error as ...Drop>::drop
core::ptr::drop_in_place<napi::error::Error>
oxfmt::core::external_formatter::wrap_format_file::{{closure}}
```
Each broken file makes the `formatFile` callback reject; the resulting `napi::Error` is dropped on the TSFN await path and reaches `napi_reference_unref` during teardown → V8 fatal check.
After this fix (callback resolves errors as data), the same workload runs clean.
leaysgur