OPM general rules for shutdowns.
https://www.opm.gov/policy-data-oversight/pay-leave/furlough-guidance/guidance-for-shutdown-furloughs.pdf
Specific updates to those rules published last week:
https://www.opm.gov/policy-data-oversight/pay-leave/furlough-guidance/addendum-to-opm-guidance-for-shutdown-furloughs.pdf
Specific rules for this shutdown.
https://www.opm.gov/policy-data-oversight/pay-leave/furlough-guidance/special-instructions-for-agencies-affected-by-a-possible-lapse-in-appropriations-starting-on-october-1-2023.pdf
That last one includes info about ‘orderly shutdown procedures”