Migrate Bun Toolchain

Identify the current and requested target version and the surfaces being changed: installation, runtime, scripts, tests, bundling, or deployment. Package manager adoption is not permission to replace the runtime or test runner. A Bun-only version upgrade does not require adopting more Bun APIs.

Read version and installation for pins, lockfile migration, dependency lifecycle trust, registries, and workspaces. Read runtime and tooling only when the runtime, tests, or bundler changes.

Use the latest stable release for an unspecified target, verified from upstream and the installed executable. Preserve an explicit target. Change every consumer of the migrated surface, not unrelated tools. Let Bun generate its lockfile and compare resolved dependencies before retiring an old installer's lockfile. Keep Node for supported scripts or dependencies that still require it.