From a monorepo commit to an over-the-air vehicle update

An engineer commits a change to the company's monorepo. Some time later, software containing that change is running on customers' cars. Describe the whole path in between: build and test, deciding what to build for which vehicle targets, packaging and signing, staged rollout, delivery over the air, installing safely on the car, and rolling back. Discuss how you would decide what needs rebuilding after a commit in a very large monorepo.