Separate DUT bugs from checker-model bugs: ordering policy, duplication, drops, and end-of-test drain.
1. Out-of-Order Responses Miscompared as Corruption [Medium]
2. Missing First Transaction After Reset [Medium]
3. Duplicate Transactions from Handle Reuse [Easy]
4. Mismatch Cascade from Incorrect Pop Policy [Hard]
5. End-of-Test Draining Missing [Hard]
6. Duplicate Expected Entries from Predictor Retry Path [Medium]Work each puzzle before reading the solution: predict the exact output or answer, name the rule that governs it, then check yourself.