Environment overrides

Two environment variables tune runs without touching the attributes — useful in CI:

Variable	Effect
PROPERTY_RUNS	Positive integer that overrides every property's run count (dial runs up in CI).
PROPERTY_SEED	Integer seed used for any property whose attribute omits seed (replay a whole suite). An explicit attribute seed still wins.
PROPERTY_VERBOSE	Any value except ''/0 logs every run's generated arguments and, on failure, every accepted shrink step (shrink step 3: x=63 -> 51) — see exactly what a replayed seed feeds the property and how the shrinker descends.
PROPERTY_DB	Directory path enabling the regression corpus (below). Unset means the feature is off and nothing is written.