merge-time-ci-economics
Merge-Time CI Economics
CI minutes are spent per trigger, not per change. Most oversized bills come from proving the same commit several times (on the branch push, on the pull request, again on the merge into the integration branch, again on the release pull request) and from paying for checks that can never change a merge decision. When a local hook already checks every commit, CI has exactly one job left: prove the commit that is about to merge. Run it once, at that moment, and make the merge wait for it.
This matters more once agents open pull requests. An agent pushes often, in small increments, and every push on a naive setup buys a full CI run that nobody reads.
The skill has two halves: measure (steps 1 to 4) and redesign (steps 5 to 10). Do not skip the first half. The fix for a bill you have not decomposed is usually a cache tweak that barely moves it.