A CLI tool that runs a project's workloads across two Bun versions and reports behavioral and performance regressions before a version bump ships

Bun's Rust rewrite introduced a new class of upgrade risk: silent runtime behavior regressions where output, module resolution, fetch semantics, or file-system behavior changes between versions without a test suite catching it. No user-facing tool exists that automates this check. This CLI installs two Bun versions side-by-side, reruns a project's own test suite and a configurable set of sample workloads against both, diffs stdout/stderr/exit codes and response payloads, and surfaces any divergence as a structured regression report. It targets backend and fullstack teams running Bun in production who need upgrade confidence before bumping .bun-version in CI.