[ericproulx]

Summary

First step toward official Falcon support: a CI job that fails if Grape stops working behind a fiber server. A README section on running Grape under Falcon comes in a separate PR.

• gemfiles/falcon.gemfile plus spec/integration/falcon, run on Ruby 3.3, 3.4 and 4.0. The file skips itself without Falcon (if: defined?(Falcon)), so the other jobs and edge.yml don't load it.
• The specs start a real Falcon::Server in-process on a free port and send it requests with async-http's client:
  • Concurrency: 30 concurrent requests, which pause in a before filter, an after filter, a custom validator inside array elements and the route block. Each keeps its own params, endpoint instance variables and validation error index.
  • error! in a child task: inside an Async task the route waits on, error! responds with its status, with and without rescue_from :all (Raise from error! instead of throwing :error #3023).
  • Streaming: stream sends each chunk of an Enumerator before the endpoint produces the next. The producer waits for the client to have each chunk, so a buffered body gets no acknowledgements, and a timeout makes that a failure instead of a hang.

Mutation check

Break	Failing spec
ParamScopeTracker on Thread#thread_variable_* instead of Fiber[]	concurrency
One endpoint shared by every request (no @prototype.dup)	concurrency
error! throwing :error instead of raising Halt	both error! specs
Halt < Exception	both error! specs
stream body read into an Array	streaming

Not covered: cancellation

A client disconnect or a server stop doesn't cancel a running endpoint. async-http 0.105's HTTP/1 and HTTP/2 servers both run the app under defer_stop, so the endpoint runs to completion (verified over HTTP/1 for both cases). There's no cancellation to spec.

Test plan

• bundle exec rake (RuboCop and the full suite) passes locally.
• BUNDLE_GEMFILE=gemfiles/falcon.gemfile bundle exec rspec spec/integration/falcon passes on Ruby 3.3.12, 3.4.9 and 4.0.9, including with --enable=frozen-string-literal, and passed 12 runs in a row on 4.0.9.
• CI green.

🤖 Generated with Claude Code

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[dblock]

Rather than putting this here, I think you should build something like grape-on-falcon, similar to https://github.com/ruby-grape/grape-on-rack, https://github.com/ruby-grape/grape-on-goliath and https://github.com/ruby-grape/grape-on-rails. We could have integration tests in grape proper, too, but then I'd add the entire spectrum of servers.