code-mode-bun-compat

Part of Oh mAI SDK, a collection of community extensions for Vercel AI SDK.

Make @ai-sdk/code-mode work under Bun. Two lines of integration, self-retiring when Bun catches up.

Quick start

bun add ai @ai-sdk/code-mode
bun add -d code-mode-bun-compat

Then wire the postinstall (after the add above — a postinstall referencing a bin that isn't installed yet fails the next install with a bare exit 127):

// package.json
{
  "scripts": {
    "postinstall": "code-mode-bun-compat"
  }
}

That's the whole integration. bun install triggers the postinstall, the installed @ai-sdk/code-mode gets patched in place (~50ms, idempotent), and code mode just works under Bun:

import { experimental_runCodeMode } from "@ai-sdk/code-mode";

const result = await experimental_runCodeMode({
  js: "return 6 * 7;",
  tools: myTools,
  options: { executionPolicy: { timeoutMs: 30_000, maxBridgeRequests: 10 } },
});

Without the patch, that import line throws under Bun before any of your code runs.

What you get

• Reinstalls are handled. Every bun install re-runs the postinstall; already-patched files are detected and skipped. A lockfile change can't silently un-patch you.
• Node stays unaffected. The shim is a runtime feature-test — on Node it finds the native API immediately, same code path as unpatched. Dual-runtime projects (dev on Bun, CI on Node) need no conditionals.
• Nothing to unwind later. When Bun ships stripTypeScriptTypes natively (PR #35517 is in progress), the feature-test starts finding the real function and the fallback simply never runs again. Delete the dep at leisure, or don't.
• Loud failure, never a weird one. If a future @ai-sdk/code-mode restructures its dist files, the patcher exits 1 with UNEXPECTED SHAPE instead of half-patching — your install fails legibly rather than your runtime failing mysteriously.
• Monorepos: code-mode-bun-compat packages/my-app resolves from a specific workspace; the bare command resolves from cwd. Resolution uses createRequire, so hoisted layouts are handled.

What it actually fixes

Two Bun gaps break @ai-sdk/code-mode today:

1. node:module has no stripTypeScriptTypes (oven-sh/bun#25058). The Code Mode runtime imports it statically in dist/utils/source-cache.js, so under Bun the import itself dies—even for programs that never feed it TypeScript. The runtime lives in @ai-sdk/code-mode in older releases and its run dependency in newer releases; the patcher resolves either layout.
2. The QuickJS worker boots from a multi-MB base64 data: URL, which Bun's module specifier canonicalization rejects (NameTooLong).

The patcher rewrites both, in place:

1. The static import becomes a feature-test with an amaro fallback. amaro is the same SWC-wasm wrapper Node itself uses for type stripping, so strip-mode output keeps Node's position-preserving semantics (types replaced in place with whitespace).
2. The data: worker URL becomes a process-private temp-file file: URL, created exclusively and removed on exit—identical worker semantics, valid in both runtimes without a shared predictable path.

Test

bun run test

Runs offline patch-shape fixtures, then installs two exact @ai-sdk/code-mode / ai pairs in isolated scratch caches: the historical in-package runtime and the extracted run layout. Both must reproduce the known Bun import failure, work natively under pinned Node, accept the patcher, accept an idempotent second run, and execute a real Bun cell end-to-end. The consumer installs the packed compatibility package and does not install amaro directly.

A separate scheduled canary installs current upstream releases and current Bun. It characterizes native support without making ordinary pull requests depend on release timing.

Scope and honesty

• This patches published dist files of a specific package shape — a bridge, not a fork. The right long-term fixes live upstream: Bun implementing the API (#35517), and/or @ai-sdk/code-mode feature-testing its import.
• Extracted from a durable agent runtime where it has been the load-bearing enabler for running code-mode cells under Bun since 2026-08.

License

Apache-2.0