Design a chain that fails safely

Your chain pulls sales data, cleans it, analyses it, drafts the summary and sends it.

Before you use the output

• The split into two chains with a human gate on the differences table is the key change. Implement that before any validation work.
• The match-rate check is the highest-value validation. A reconciliation matching on the wrong key produces plausible output and is otherwise undetectable.
• Rows-in versus rows-out logging at every stage costs almost nothing and is the first thing you will look at when something is wrong.
• Test each stage in isolation with deliberately broken input before testing end to end.