A byte fuzzer pointed at a structured input spends most of its budget on inputs the decoder throws away. nelli mutates the typed choice sequence directly, so every mutant is valid by construction, and it uses a comparison log to defeat magic-value branches exactly.
nelli is a Nim testing library built on a choice-sequence engine. Because a test input is just a recorded sequence of typed choices, the same engine drives property testing, coverage-guided fuzzing, and SMT-backed symbolic execution.
PresenceLock locks your Windows session when you step away from the webcam. The lock decision is a pure F# function of state, time, and events, with no clocks and no I/O, so the part that matters is testable without a camera or Windows at all.