ci: onboard Blacksmith Testbox

.github/actionlint.yaml

@@ -19,4 +19,5 @@ self-hosted-runner:
     # Linux: Blacksmith primary (LINUX_RUNNER), WarpBuild overflow fallback.
     - blacksmith-4vcpu-ubuntu-2404
     - blacksmith-8vcpu-ubuntu-2404
+    - blacksmith-32vcpu-ubuntu-2404
     - warp-ubuntu-latest-x64-4x

.gitignore

@@ -73,3 +73,7 @@ artifacts/
 
 # tmux verbose debug logs (tmux -v) that land in the cwd
 tmux-*.log
+
+# Remote-only Blacksmith cmux-tui benchmark output
+/testbox-benchmark/
+/.cmux-scratch/

scripts/blacksmith-bounded-command.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [[ $# -lt 2 || ! "$1" =~ ^[0-9]+$ ]]; then
+  echo "usage: $0 <timeout-seconds> <command> [args...]" >&2
+  exit 64
+fi
+seconds="$1"
+shift
+
+# Prefer GNU coreutils when present, while keeping the operator workflow
+# usable on macOS hosts that have neither `timeout` nor `gtimeout`.
+for candidate in gtimeout timeout; do
+  if command -v "$candidate" >/dev/null && "$candidate" --version 2>&1 | grep -q 'GNU coreutils'; then
+    exec "$candidate" --kill-after=5s "${seconds}s" "$@"
+  fi
+done
+
+exec python3 - "$seconds" "$@" <<'PY'
+import os
+import signal
+import subprocess
+import sys
+
+seconds = float(sys.argv[1])
+argv = sys.argv[2:]
+if not argv:
+    raise SystemExit("missing command")
+process = subprocess.Popen(argv, start_new_session=True)
+try:
+    raise SystemExit(process.wait(timeout=seconds))
+except subprocess.TimeoutExpired:
+    os.killpg(process.pid, signal.SIGTERM)
+    try:
+        process.wait(timeout=5)
+    except subprocess.TimeoutExpired:
+        os.killpg(process.pid, signal.SIGKILL)
+        process.wait()
+    raise SystemExit(124)
+PY