## Summary
- Fixed HTMLRewriter to throw proper errors instead of `[native code:
Exception]`
- The issue was incorrect error handling in the `transform_` function -
it wasn't properly checking for errors from `beginTransform()`
- Added proper error checking using `toError()` method on JSValue to
normalize Exception and Error instances
## Test plan
- Added regression test in `test/regression/issue/19219.test.ts`
- Test verifies that HTMLRewriter throws proper TypeError with
descriptive message when handlers throw
- All existing HTMLRewriter tests continue to pass
Fixes#19219🤖 Generated with [Claude Code](https://claude.ai/code)
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
