Patch release. The shellcheck reusable now uses the runner's preinstalled ShellCheck with a guarded apt fallback (a stalled apt mirror was silently wedging required checks for 20+ minutes — three times on 2026-08-19; #53), and carries a 5-minute job timeout backstop. Internal composite-action refs bumped to v1.2.2 per RELEASING.md. No input or contract changes.