HTTP Trailer support?

Has anyone successfully sent http trailers from a worker response?

I’ve been computing Server-Timing [1] headers for returning metrics & (limited) timing info, which works fine for buffered responses - but for streaming responses, they are only really useful after the body.

It’s not clear how to send these using the fetch response api.

[1] https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Server-Timing