What did your last silent failure actually cost you?

Workflows that finish green while nothing happened — the threads are full of them. What I can’t find anywhere is the money.

1. When it last happened — what did it cost? Refund, lost client, hours of digging? What kind of workflow was it?

2. Did you build something for it afterwards, or decide it wasn’t worth the time?

3. Have you ever paid for a tool specifically to catch this? If yes, what and how much. If no, what would have had to be true?

Asking because one person here told me diagnosing this is billable work for a consultancy, so a tool that shortens diagnosis shortens the invoice. Someone else said it’s unbillable firefighting. Opposite answers, and I can’t tell which is more common.

“It cost nothing and I’d never pay for a tool to catch it” is a real answer — if it’s true, it’s the most useful one.