Joël Quenneville
Principal developer at thoughtbot, Boston, and the speaker who put the name on harness-engineering for the Ruby world. His Rails World 2026 talk, “Harness Engineering on Rails” (2026-09-24), made the argument that an agent is a loop, that the quest to one-shot your code with the perfect prompt is a trap, and that the reaction to mediocre code should be fixing the harness rather than the mistake, which is what makes the agent usable https://rubyonrails.org/world/2026/sessions/harness-engineering. The talk’s practical direction moves judgment out of AGENTS.md prose and into deterministic machinery, custom RuboCop cops, generators, hooks, focused review skills, domain-specific scripts https://www.rubyevents.org/talks/harness-engineering-on-rails. He co-hosts the podcast “The Bikeshed” and posts as @joelquen https://rubyonrails.org/world/2026/speakers/joel-quenneville.
The talk landed in a moment. An attendee recap at Telos Labs reports “harness” was heard “in nearly every room” at Rails World 2026, and credits Quenneville’s feed-forward versus feedback split as the framework people carried out. Ryan’s notes on the talk, written 2026-10-16 before this page existed, ported the same 2x2 to Rust and found the rustc-dev-guide’s “Reviewing code with LLMs” page stating the same ladder independently. The video itself has no English caption track, which is why this page cites written material only. See 2026-09-24-quenneville-harness-engineering-rails-world.
Sources
- Session and speaker pages at rubyonrails.org, read 2026-10-25: https://rubyonrails.org/world/2026/speakers/joel-quenneville
- Indexed talk summary: https://www.rubyevents.org/talks/harness-engineering-on-rails
- Telos Labs recap, 2026-10-09: https://teloslabs.co/post/rails-world-2026-harnesses-agents-judgment