Localize hang roots in sequence-driver handshakes, phase ownership, and missing completion signals.
1. Handshake Hang: Missing item_done on One Branch [Medium]
2. Missing run_phase Objection in Test [Easy]
3. Wrong Phase: Starting Traffic in shutdown_phase [Medium]
4. Handshake Violation: item_done Called Twice [Medium]
5. Sequence get_response Stall [Hard]
6. Virtual Sequence Waits on Event Never Triggered [Hard]Work each puzzle before reading the solution: predict the exact output or answer, name the rule that governs it, then check yourself.