what doesn't match up? seems fine to me on a quick read
what doesn't match up? seems fine to me on a quick read

wrangler secret put CALLS_APP_SECRET you dont need to specify the value in the command. you will write the value when it asks for the secret value/ is marked as a document, /abc.js is marked as js)
Does returning response with status code 500 automatically send this page?Nope
fetch Responses within a Worker?node_compat involves bundling polyfills into your Worker. nodejs_compat are native Node-ish modules that you can use without changes to your Worker itself. Wherever possible, we recommend the compat flag, but some packages require node_compat insteadcontent-length off