The fuzz corpus

Every level spec the generators ever failed on, as npm run level:fuzz wrote it out (a file with its label, its failure and the whole spec), kept once the generator is fixed so the fault never comes back: npm run level:fuzz -- --corpus builds each again, and the Release workflow does before a release is published. A spec that needs Blender (a grid town, a region with towns) is skipped where Blender is not found and said so.

To add one: copy the file the failing run uploaded (the nightly Level fuzz workflow's fuzz-failures artifact, or fuzz-failures/ of a local run) here, under a name that says what it caught, once npm run level:fuzz -- --replay <file> passes. See Quality gates.