model

type Model[S any] struct {
	// Key returns a dedup key. Two states with the same key are the same state.
	Key func(S) string
	// Successors returns every enabled action from s. An empty result means s
	// is terminal.
	Successors func(S) []S
	// Quiescent reports whether a terminal state is a legal stopping point.
	// A terminal state that is not quiescent is a deadlock.
	Quiescent func(S) bool
	// CheckTerminal validates one terminal state. Return an error to fail.
	CheckTerminal func(S) error
}

type Report struct {
	Explored  int
	Terminals int
}