UnboundMethod#arity compatibility issue with Ruby 3.4.4 causes deployment failures

[SeanLF]

Description of the issue

After upgrading from Ruby 3.4.3 to 3.4.4, my Sinatra application fails to start with Falcon when deployed via Dokku. The failure occurs specifically in UnboundMethod#arity inside async-service gem.

Environment

• Ruby version: 3.4.4
• async-service gem version: 0.13.0
• async-container gem version: 0.24.0
• falcon gem version: 0.51.1
• Deployment: Dokku (container-based)

Error details

The application fails during initialization with the following error:

-----> Executing 2 healthchecks
       Running healthcheck name='web check' delay=0 path='/health/ready' retries=9 timeout=5 type='path'
       Running healthcheck name='port listening check' attempts=3 port=5000 retries=2 timeout=5 type='listening' wait=5
remote:  !     Failure in name='web check': Get "http://172.17.0.5:5000/health/ready": dial tcp 172.17.0.5:5000: connect: connection refused
       Healthcheck succeeded name='port listening check'
04a9a989668db9f48ebf9be034cabc39b15c59d498d78d54f37612f6586e8665
remote:  !     Could not start due to 1 failed checks (web.1)
=====> Start of *********** container output (04a9a989668d web.1)
       {"time":"2025-05-17T23:18:59+00:00","severity":"info","oid":1024,"pid":12,"subject":"Falcon::Command::Host","message":"Falcon Host v0.51.1 taking flight!\n- Configuration: falcon.rb\n- To terminate: Ctrl-C or kill 12\n- To reload: kill -HUP 12\n"}
       {"time":"2025-05-17T23:19:00+00:00","severity":"info","oid":1032,"pid":12,"subject":"Async::Container::Notify::Console","message":{"status":"Initializing controller..."}}
       {"time":"2025-05-17T23:19:00+00:00","severity":"info","oid":1048,"pid":12,"subject":"Falcon::Service::Server","message":"Preloading preload.rb..."}
       {"time":"2025-05-17T23:19:00+00:00","severity":"info","oid":1048,"pid":12,"subject":"Falcon::Service::Server","message":"Starting app on #<Async::HTTP::Endpoint http://0.0.0.0:5000/ {protocol: Async::HTTP::Protocol::HTTP11}>"}
       {"time":"2025-05-17T23:19:00+00:00","severity":"info","oid":1224,"pid":12,"subject":"Async::Service::Controller","message":"Controller starting..."}
       {"time":"2025-05-17T23:19:00+00:00","severity":"info","oid":1248,"pid":12,"subject":"Async::Container::Group","message":"Sending terminate to 1 running processes..."}
       {"time":"2025-05-17T23:19:01+00:00","severity":"error","oid":1232,"pid":164,"subject":"Async::Container::Forked::Child","message":"SIGTERM","event":{"type":"failure","root":"/app","class":"Async::Container::Terminate","message":"SIGTERM","backtrace":["/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:105:in 'Thread#raise'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:105:in 'block (3 levels) in Async::Container::Forked::Child.fork'","/app/vendor/bundle/ruby/3.4.0/gems/async-service-0.13.0/lib/async/service/environment.rb:125:in 'UnboundMethod#arity'","/app/vendor/bundle/ruby/3.4.0/gems/async-service-0.13.0/lib/async/service/environment.rb:125:in 'block in Async::Service::Environment::Evaluator.wrap'","/app/vendor/bundle/ruby/3.4.0/gems/async-service-0.13.0/lib/async/service/environment.rb:121:in 'Array#each'","/app/vendor/bundle/ruby/3.4.0/gems/async-service-0.13.0/lib/async/service/environment.rb:121:in 'Async::Service::Environment::Evaluator.wrap'","/app/vendor/bundle/ruby/3.4.0/gems/async-service-0.13.0/lib/async/service/environment.rb:171:in 'Async::Service::Environment#evaluator'","/app/vendor/bundle/ruby/3.4.0/gems/falcon-0.51.1/lib/falcon/service/server.rb:59:in 'block in Falcon::Service::Server#setup'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:110:in 'block (3 levels) in Async::Container::Forked::Child.fork'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:109:in 'Thread.handle_interrupt'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:109:in 'block (2 levels) in Async::Container::Forked::Child.fork'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:102:in 'Process.fork'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:102:in 'block in Async::Container::Forked::Child.fork'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:146:in 'Async::Container::Forked::Child#initialize'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:101:in 'Class#new'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:101:in 'Async::Container::Forked::Child.fork'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/forked.rb:262:in 'Async::Container::Forked#start'","/app/vendor/bundle/ruby/3.4.0/gems/async-container-0.24.0/lib/async/container/generic.rb:176:in 'block in Async::Container::Generic#spawn'"]}}
       {"time":"2025-05-17T23:19:01+00:00","severity":"error","oid":1256,"pid":12,"subject":"Async::Container::Forked","status":"pid 164 exit 1"}
=====> End of ********* container output (04a9a989668d web.1)
remote: parallel: This job failed: