REST API POST response body?

I'm using a REST API block to POST a rich message to Slack. I'd like to thread some replies, which requires reading an ID from the POST response and including it on a subsequent request.

In the code editor, the autocomplete options I get from the REST API block don't seem to include the HTTP response. I see a .data.message that always contains "ok", and I see which appears to contain the request URL/method/body, the response headers, and status and statusText response values, but no response body.

Related, if the REST API block fails, it stops the workflow dead. I'd like to process the error, but execution never reaches the next block. I see you can designate a global error handler, but I don't see anything in the docs about how you reference the error inside the handler, or figure out which block it came from. What's the best way to handle REST API errors in a workflow?