The `custom-image-*` workflows trigger on any `push` with no `branches:` filter, check out the pushed ref, and run repo-local scripts (`./scripts/clean-storage-linux.sh` / `clean-storage-win.ps1`) on persistent self-hosted runners (`unreal-image-creating-runner-*`) whose disk is captured via `snapshot:` into a base image reused by future jobs. A contributor with write access can push a modified script to any feature branch to execute code on the runner before the snapshot boundary, persistently poisoning every downstream runner image. Add a `branches: [main]` filter so only trusted refs build the images.