This patch improves random generation for tests with repeated structure (recursive generators, collections, state machines). The engine proposes new test cases by splicing the choices of one span over another with the same label; a spliced sequence that diverged from its donor's path was previously discarded, and is now completed with fresh random draws instead, so every such proposal becomes a real test case seeded with the mutation.
libhegel C ABI
This patch improves the generation phase's span mutation. A mutated choice sequence that diverges from its donor's path previously ran out of data and was discarded as an overrun; mutation probes now draw randomly past the end of the spliced choices, so a diverged proposal becomes a complete test case seeded with the mutation. On recursive-generator workloads this turns a substantial fraction of previously wasted probes into productive test cases.