WASM + File System API + output

I just experimented with the esbuild WASM module and was able to resolve paths to local file system using the File Access API.
What I am missing: how to control esbuild to write output files directly to my file sys handle. Essentially, I am missing a build.onOutput() callback. I think it would be better to stream the output using this callback than providing in-memory buffers in the build result.
Any thoughts?

The issue mentions esbuild's WASM module, the browser File Access API, and in-memory build results, but names no files or tests. Start by tracing the WASM build interface and current output handling; done would mean determining a supported way to send output to a supplied file-system handle.

Written by the indexing model from the issue text.