CircleCI has a maximum of 1 macOS runner, so it's important that we optimise running time.

Expensive operations:

• iOS builds
• iOS test runs
• Brew update

We could use something like folder-hash and storing artifacts to see if anything important has changed and, if not, save rebuilding by using a previously built iOS app. We might be able to optimise further on branch name or something?

Similarly, could brew caches be preserved between pipeline runs? Rather than going zero -> latest every time, maybe this could be quicker if we're updating from something more recent? It's an external dependency, so branch doesn't matter.