tl;dr: Bun's creator used Claude (a pre-release "Fable 5" model) to mechanically port Bun's ~535k lines of Zig to Rust over 11 days, aiming to eliminate a recurring class of memory bugs (use-after-free, leaks) that stemmed from mixing GC'd JS values with Zig's manual memory management. The workflow used ~50 parallel loops with strict separation between implementer and adversarial reviewer Claudes (in isolated context windows), compiler errors as a work queue across 64 agents, and Bun's existing TypeScript test suite as language-independent ground truth. All CI shards eventually went green and the rewrite was merged.