Harden worker queue and restore drill defaults

tools/checks/module-installer-rollback-drill.py

@@ -14,6 +14,7 @@ import sys
 import tempfile
 from collections.abc import Callable, Iterable
 from contextlib import contextmanager
+from datetime import UTC, datetime
 from pathlib import Path
 from types import SimpleNamespace
 from typing import Any
@@ -65,6 +66,11 @@ def main() -> int:
     parser.add_argument("--runtime-root", type=Path, help="Directory for temporary drill runtimes. Defaults to a new temp directory.")
     parser.add_argument("--keep-runtime", action="store_true", help="Keep the temporary drill runtime after completion.")
     parser.add_argument("--format", choices=("json", "text"), default="text", help="Output format.")
+    parser.add_argument(
+        "--evidence-path",
+        type=Path,
+        help="Write an atomic machine-readable drill result for the Ops health surface.",
+    )
     args = parser.parse_args()
 
     runtime_root = args.runtime_root or Path(tempfile.mkdtemp(prefix="govoplan-installer-drill-"))
@@ -88,7 +94,14 @@ def main() -> int:
         if not args.keep_runtime and args.runtime_root is None:
             shutil.rmtree(runtime_root, ignore_errors=True)
 
-    payload = {"ok": ok, "runtime_root": str(runtime_root), "scenarios": results}
+    payload = {
+        "ok": ok,
+        "completed_at": datetime.now(tz=UTC).isoformat(),
+        "runtime_root": str(runtime_root),
+        "scenarios": results,
+    }
+    if args.evidence_path:
+        _write_evidence(args.evidence_path, payload)
     if args.format == "json":
         print(json.dumps(payload, indent=2, sort_keys=True))
     else:
@@ -105,6 +118,18 @@ def main() -> int:
     return 0 if ok else 1
 
 
+def _write_evidence(path: Path, payload: dict[str, object]) -> None:
+    path = path.expanduser()
+    path.parent.mkdir(parents=True, exist_ok=True)
+    temporary = path.with_suffix(path.suffix + ".tmp")
+    temporary.write_text(
+        json.dumps(payload, indent=2, sort_keys=True) + "\n",
+        encoding="utf-8",
+    )
+    temporary.chmod(0o600)
+    temporary.replace(path)
+
+
 def package_failure(root: Path) -> dict[str, object]:
     database_url, database = _sqlite_database(root)
     plan = _saved_install_plan(database, "package-failure-example")