onsager-pre-push

Run before pushing code to the Onsager repo to catch what CI would fail on, and confirm the branch has a linked spec issue in a valid state. Reproduces CI's merge preview + strict-warnings environment, renumbers colliding migrations, and walks through the repo's common merge-conflict patterns. Triggers include "before push", "ready to push", "pre-push check", "push readiness", "prep for PR", "resolve merge conflict", "merge conflict", "branch has conflicts", "sync with main", or proactively before any git push on an Onsager branch.