- nh_login_preflight (platform.sh): sources with credentials at
  $CONF_DIR/logins/<source>.json (600) get a login check via the
  skill's login-tools.js before claude runs; auto-login on failure;
  harvest never blocked (paywall honestly reported by result contract)
- harvest.sh invokes preflight after result contract preparation
- SKILLS_DIR / SKILLS_REPO_URL documented in default.conf.example
- test: preflight invoked when credentials configured (fake skill)