We migrated a large native iOS and Android app to a Flutter monorepo and built the CI/CD infrastructure from scratch — GitHub Actions for CI, Codemagic for CD, and Melos holding the monorepo together. This talk covers the architecture decisions that made the pipeline fast and reliable: path-based triggers that only run what changed, parallelized test execution across four threads with randomized ordering, 100% coverage enforcement as a gate (not a goal), and ephemeral build environments with smart caching that keep things reproducible without being slow. We'll walk through how a five-layer package structure with strict dependency rules enables per-package workflows that scale. You'll leave with a practical framework for building Flutter monorepo CI/CD that gives your team fast feedback loops, clean environments, and confidence that what passes CI is ready to ship.