Request for a method to wrap executing @block in Endpoint

Hi, I work on the Elastic APM Ruby agent. We've recently added support for instrumenting Grape apps and it will be released in our next minor version.

Right now, we do not have backtraces for spans with Grape because using caller in our ActiveSupport::Notifications subscriber will not show a backtrace leading to the user's code. It instead shows this (note this isn't the complete backtrace, just the top ~20 lines):

/Users/emily/.rvm/gems/ruby-2.6.2/gems/activesupport-6.0.1/lib/active_support/notifications/fanout.rb:156:in `start'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/activesupport-6.0.1/lib/active_support/notifications/fanout.rb:58:in `block in start'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/activesupport-6.0.1/lib/active_support/notifications/fanout.rb:58:in `each'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/activesupport-6.0.1/lib/active_support/notifications/fanout.rb:58:in `start'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/activesupport-6.0.1/lib/active_support/notifications/instrumenter.rb:36:in `start'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/activesupport-6.0.1/lib/active_support/notifications/instrumenter.rb:22:in `instrument'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/activesupport-6.0.1/lib/active_support/notifications.rb:180:in `instrument'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/grape-1.2.4/lib/grape/endpoint.rb:243:in `run'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/grape-1.2.4/lib/grape/endpoint.rb:318:in `block in build_stack'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/grape-1.2.4/lib/grape/middleware/base.rb:31:in `call!'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/grape-1.2.4/lib/grape/middleware/base.rb:24:in `call'
/Users/emily/Code/apm-agent-ruby/fork/apm-agent-ruby/lib/elastic_apm/middleware.rb:20:in `call'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/grape-1.2.4/lib/grape/middleware/error.rb:37:in `block in call!'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/grape-1.2.4/lib/grape/middleware/error.rb:36:in `catch'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/grape-1.2.4/lib/grape/middleware/error.rb:36:in `call!'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/grape-1.2.4/lib/grape/middleware/base.rb:24:in `call'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/rack-2.0.7/lib/rack/head.rb:12:in `call'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/grape-1.2.4/lib/grape/endpoint.rb:227:in `call!'
/Users/emily/.rvm/gems/ruby-2.6.2/gems/grape-1.2.4/lib/grape/endpoint.rb:221:in `call'

You call the user's code on this line so I'm asking if you can maybe wrap that in another method. That way, we can alias the method, grab the stacktrace with caller, then call the original method.
If you have other ideas on how to expose the stacktrace, we are open to hearing them. Let me know what you'd prefer and I'm happy to open a PR.
Thanks in advance!

Read lib/grape/endpoint.rb around the user-code call at line 263 and trace how the endpoint executes @block. Determine how a method boundary could expose the caller backtrace without changing endpoint behavior. Done means the Elastic APM use case can capture a backtrace leading to the user's code, with the approach validated against the existing endpoint flow.