Stacked PRs, Ghost Merges, and the Merge Box: Inside GitHub's Biggest Pull Request Change in Years

Cassidy and Andrea are joined by Sameen Karim, Senior Product Manager at GitHub, to dig into stacked pull requests, GitHub's newly launched (and long-requested) way to break large changes into a linked chain of small, reviewable PRs. Sameen pulls back the curtain on just how deep this went: every time a PR updates, GitHub runs a live "ghost merge" simulation behind the scenes to check whether it's mergeable, and stacking meant multiplying that complexity across up to 100 linked PRs at once. The team had to rethink core assumptions about how a PR's base branch relates to its actual merge…