A sandbox at its memory limit stays reachable, and every process killed for memory is recorded

Linux's out-of-memory killer now never ends Runtime's agent or the sandbox's network relay, so commands keep running after a kill. Each process it ends, inside a command or not, is recorded as the event sandbox.oom_kill with its name, process ID and memory. The event is shown on the sandbox's page in the console and sent to webhooks. When the agent does not answer, the API returns sandbox_unreachable (503, retryable), and names a recent out-of-memory kill when there was one. When the sandbox cannot read its environment, the API returns sandbox_environment_unavailable (503, retryable). Both replace guest_busy, which now means only that the sandbox is running as many commands as it can. POST /v1/sandboxes/{id}:restart on a running sandbox now reboots it from its disk instead of returning 409 not_resumable. See troubleshooting.