DevOps Engineer: Stop planned maintenance from paging on-call

You're done when

• Silences made with bin/sentinella silence add (and shown and ended with list and delete) work as CONTRACT.md §4 says, hold only the alerts they match, survive a restart and work on a database already at schema version 2, as production's is; with no silence, Sentinella pages exactly as before and Rita's locked tests pass.
• While a silence is active, nobody is paged for the alerts it matches, for as long as it lasts, on nights you have not seen and in Rita's replay, except where the rule Agnese sends while you work says otherwise; that rule holds for every alert it covers, and the silences it forbids are refused.
• When a silence ends, Sentinella does what you chose in the decision Agnese leaves you, and DECISIONS.md starts with that decision and your reasons.
• Your tests pass on a correct Sentinella that follows your decision, and fail on versions that break a rule.
• DECISIONS.md has, under ## Replay, the numbers of two replays you ran yourself on your final Sentinella: last Saturday without a silence, and Rita's sign-off replay.

What it measures

Your environment