Discovery / Differential bug hunting
Ledger investigation
Design experiments that expose two hidden faults in apparently similar account systems.
The two ledgers
Two implementations disagree with the contract under different conditions. Build a reproducing trace for each, then identify both defects.
One hold at a time. Reserve charges a 1-unit fee. Commit before clock 2 credits the recipient. At clock 2 or later, commit refunds principal and fee. Cancel and restart refund both. Wait advances one tick. Every experiment resets all four accounts.
File your findings
Moss witnessStill needed
Fern witnessStill needed
Experiment, make a prediction, and check your solution when ready.
Need a hint?
Probe the exact expiry boundary. Separately compare cancelling a small and a larger reservation.