Building an Android app outside the network it had to run inside
An Android app for an air-gapped factory network was built on a machine outside that network, then carried in by hand. When it failed inside, there was no way to see why from where the build happened.
The app targeted a closed network on a factory floor, the kind with no route in or out. The build machine sat outside that network, because that was the machine that had one. So the loop went: build the artifact outside, copy it across the boundary by hand, install it inside, watch it fail, copy it back out in my head, change something, build again.
The artifact behaved differently inside than anything I could reproduce outside. Each pass cost a walk across the boundary and a guess about what the difference was, and a single round could eat most of an afternoon. Nothing about the failure was visible from where the build ran.
The fix is flat enough to state as one line.
Build inside the network it runs in, or run a reproducible pipeline that targets that network, so "builds outside, runs inside" stops being a guessing loop.
There was no build environment inside the network at the time. So there was no such step.