Diagnose closure stalls by separating true stimulus gaps from unreachable bins and sampling-region mistakes, then read metrics correctly across instances.
1. Sampling region off-by-one on state bins [Medium]
2. Unreachable bin from stimulus constraints [Easy]
3. Manual sample called at wrong phase [Hard]
4. get_coverage vs get_inst_coverage interpretation [Medium]
5. Unreachable cross tuple from protocol rules [Hard]
6. at_least threshold causes closure plateau [Medium]Work each puzzle before reading the solution: predict the exact output or answer, name the rule that governs it, then check yourself.