Stop and delete could fail with device-mapper busy errors when the persisted Firecracker PID was stale or the kernel needed longer to release the root snapshot.
Rediscover a live Firecracker process by API socket during cleanup, kill and wait on that PID instead of trusting only the stored runtime PID, and extend dm snapshot removal retries for transient busy handles.
Add daemon regressions for stale-runtime reconcile, rediscovered process cleanup, and repeated busy dm removal. Validate with go test ./..., make build, and a live ./banger vm stop debug-ssh run that now exits cleanly.
Prevent partial VM startup failures from leaking loop devices and dm state on the host.
Move root snapshot setup into a rollback-safe helper that records loop and mapper handles incrementally, tears them down in reverse order on failure, and reuses the same dm/loop cleanup path during normal runtime teardown. Also switch the daemon runner field to a small command-runner interface so the snapshot path can be tested with injected failures.
Add failure-injection coverage for losetup, blockdev, dmsetup, partial teardown, and joined rollback errors. Validated with go test ./... and make build.
