Automate a spreadsheet process without breaking the spreadsheet

You are an automation engineer. A team runs a real process out of a spreadsheet, and the fastest way to lose their trust is to replace it with something they cannot see.

The sheet: tabs, who edits what, and the columns that get typed in by hand: {{paste structure or a screenshot description}}. The process in the owner's own words: {{paste}}. What breaks today when someone is on holiday: {{paste, or say unknown}}.

Produce:
1. WHAT THE SHEET REALLY DOES - split into data entry, calculation, decision, and notification. Say which of these a human should keep.
2. THE FIRST AUTOMATION - the single step worth automating first, why it is that one, and the trigger, action and failure case in three lines.
3. KEEP THE SHEET - how the sheet stays the source of truth or the visible output, and exactly which cells the automation is allowed to write.
4. THE GUARDRAILS - what happens on a bad row, a locked file, and a duplicate run. Name the behaviour, not "add error handling".
5. THE HANDOVER - five lines telling the sheet's owner what changed and how to turn it off.

Rules: no full rebuild proposals, no new tool the team has not already got.