Fill the responsibility inventory: installation and lockfile, the runtime each script really starts, test runner, bundler, CI setup, and image. Mark which rows the request moves.
Pin the Bun version the user named and print bun --version and bun --revision wherever it runs (version selection).
Run the current workflow once in a disposable copy and record the test count, build outputs, and the runtime shown at startup.
Package manager: run bun install with the old lockfile present so migration converts it. Then run scripts/compare_lockfiles.py (comparison) and explain every changed line before you delete the old lockfile.
Review blocked lifecycle scripts with bun pm untrusted. Trust only packages whose script you read (trust). Record the linker and configVersion (linker).
Runtime, tests, or bundler: apply only the requested cards in runtime, tests, and bundling.
Replace CI installs with bun ci. Also add the workspace edge check for workspaces. Update each CI setup step, image, and document that names the old tool, and leave the rest unchanged.
Run every moved command on the migrated tree. Report the results, the rollback unit, and the remaining compatibility gaps.

Route the evidence to a card

Evidence or request	Card
"Switch to Bun", unclear scope	Responsibility inventory
Pinning or upgrading Bun only	Version selection
`package-lock.json`, `yarn.lock`, `pnpm-lock.yaml` present	Automatic migration
Need to prove versions did not move	Resolution comparison
`bun.lockb` in the repository	Binary lockfile conversion
CI install should fail on drift	Frozen installs
Workspace repository, new internal dependency	Workspace edge gap
`Blocked N postinstall`, missing native binary	trustedDependencies
Import works locally, fails when published	Linker
Private registry, scoped packages, tokens	Registries
Scripts must run on Bun, or must stay on Node	bun run and --bun
"Run the server on Bun"	Direct entry, Node boundary
Jest or `node:test` suite to `bun test`	Test runner, setup and coverage
esbuild, Rollup, or webpack to `bun build`	Bundler target
Undo plan	Rollback unit

Rules

Moving the package manager does not move the runtime. bun run keeps a script's node command on Node. Add --bun only when the request moves the runtime.
Never run bun update or delete the old lockfile to get past an install error. Only a comparison with an explained result lets a version change in.
CI installs use bun ci, which is the same as bun install --frozen-lockfile. In workspaces, also run bun install --lockfile-only followed by git diff --exit-code bun.lock, because frozen installs miss new workspace:* edges.
Put a package in trustedDependencies only after reading its install script. A list replaces Bun's built-in trusted list. file:, git:, and link: sources always need an explicit entry.
Keep registry tokens in environment variables. Never switch a private scope to the public registry.
Keep type checking (tsc --noEmit) as its own step. Bun runs TypeScript without checking types.
Do not run bun test --update-snapshots to make a suite pass. Review each snapshot change.
A green install proves only that the install worked. Show a real run of every moved command before claiming the migration works.

scripts/compare_lockfiles.py OLD NEW [--json] diffs the resolved versions between package-lock.json (v2/v3) and bun.lock. It exits 0 when they are the same, 1 on a difference, and 2 on bad input or a graph with nested versions (then diff bun pm ls --all instead). scripts/test_compare_lockfiles.py holds its tests.
assets/examples/npm-project/ is the npm workspace before the migration, with package-lock.json. assets/examples/fixture/ is the same workspace written for Bun (workspace:*).
sh assets/examples/verify.sh exercises every card offline in a temporary copy. BUN, NODE, and PYTHON override the executables.

Package manager: inventory, version, lockfile migration and comparison, bun.lockb, frozen installs, the workspace gap, lifecycle trust, linker, and registries.
Runtime, tests, and bundling: bun run versus --bun, direct entry, the Node compatibility boundary, bun test, preload, coverage and JUnit output, the bun build target, and rollback.

A responsibility table that lists each row as moved or kept, with the command that proves it.
The Bun version and revision from every environment that runs it.
compare_lockfiles.py output or the bun pm ls --all diff, with every change explained.
The bun pm untrusted result and the trusted packages, with a reason for each.
Test counts before and after, build artifacts checked on their consumer, and the runtime observed at startup.
The CI diff, the rollback command, and known gaps, each marked Executed, Compiled, or Not runnable here.

The request does not say whether the runtime moves, and production runs the affected scripts.
The comparison shows changed versions that the user did not approve.
A registry needs credentials that are not available.
A required API, Jest feature, or bundler plugin is unsupported in the selected Bun version.