A build that passed isn't an instance that runs

A green build is satisfying. It's also not the finish line. The build turns your repository into something runnable; the run is whether that something actually starts, stays healthy and serves traffic.

Build time

Image selection, provisioning, networking and health checks. If this fails, you get BUILD_FAILED and the logs that explain it.

Run time

The running instance, its CPU and memory, disk and network behaviour. If the rollout fails you'll see START_FAILED; if a running instance falls over, STOPPED.

CREATING → BOOTING → RUNNING

CREATING  ✕ BUILD_FAILED
BOOTING   ✕ START_FAILED
RUNNING   ✕ STOPPED

Separating these states means the instance screen can stay simple while still telling you the truth about what happened.