Every dynamic import fails under experimental.bundledDev with vite 8.3.0 + rolldown 1.2.9: __rolldown_runtime__.requestLazy is not a function #23547

Describe the bug

With experimental.bundledDev: true, any dynamic import() throws at runtime:

TypeError: __rolldown_runtime__.requestLazy is not a function

rolldown 1.2.9 emits a call to __rolldown_runtime__.requestLazy(...) for lazy chunks, but the dev runtime Vite 8.3.0 serves to the browser has no such method.

vite/dist/client/bundledDevClient.mjs inlines its own copy of rolldown's DevRuntime. That copy has:

registerGraph, registerFactory, registerModule, getImporters, isExecuted, hasFactory, removeModuleCache, initModule, loadExports, createModuleHotContext

rolldown 1.2.9's dist/experimental-runtime.mjs has all of those plus requestLazy. requestLazy is new in 1.2.9 — 1.2.6, 1.2.7 and 1.2.8 do not have it:

vite 8.3.0 declares "rolldown": "~1.2.6", so a fresh install resolves rolldown 1.2.9 and the emitted code and the shipped runtime disagree. Both are the current latest, so I think anyone installing today hits this.

Generated chunk, straight off the dev server:

//#region src/main.js
var main_exports = /* @__PURE__ */ __exportAll({});
const main_hot = __rolldown_runtime__.createModuleHotContext("src/main.js");
__rolldown_runtime__.registerModule("src/main.js", { exports: main_exports });
…
const data = await __rolldown_runtime__.requestLazy("src/data.json", () => import(`/@vite/lazy?id=…&clientId=${__rolldown_runtime__.clientId}`));

The other three calls on the same object resolve fine — it is only requestLazy that is missing.

Pinning rolldown to 1.2.6 makes it work again, which I think confirms the diagnosis:

{ "overrides": { "rolldown": "1.2.6" } }

It is not JSON-specific — a dynamic import of a plain .js module fails the same way. Without bundledDev both work.

For scale, on the app I hit this in there are 196 such call sites in the dev bundle: a syntax-highlighting package's language modes, a diagramming package's diagram types, PDF and zip libraries, and the React.lazy route split. The routes are what makes it fatal — the app never leaves its loading screen. Pinning 1.2.6 fixes all of it and is what we shipped as a workaround.

Possible fixes, whichever you prefer: regenerate the inlined runtime in bundledDevClient.mjs against 1.2.9, or tighten the dependency range so a rolldown that emits requestLazy cannot be paired with a runtime that lacks it.

I did not find an existing issue for this in vitejs/vite or rolldown/rolldown.

Reproduction

https://gist.github.com/yeefun/1adc0939eca523331ba6ea01265a0463

Seven small files, no framework and no plugins. Gists are flat, so the README.md there says which files belong under src/.

Steps to reproduce

1. Recreate the file layout from the gist's README.md.
2. npm install
3. npm run dev
4. Open the page.

It shows:

json: FAILED __rolldown_runtime__.requestLazy is not a function | js: FAILED __rolldown_runtime__.requestLazy is not a function

Remove experimental.bundledDev and both load fine.

System Info

  System:
    OS: macOS 26.6.2
    CPU: (10) arm64 Apple M1 Pro
    Memory: 174.66 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.22.3
    Yarn: 1.22.22
    npm: 10.9.8
  Browsers:
    Chrome: 153.0.8010.53
    Firefox: 126.0.1
    Safari: 26.6.2
  npmPackages:
    vite: 8.3.0 => 8.3.0
    rolldown: 1.2.9 (transitive, from vite's `~1.2.6`)

Used Package Manager

npm (also reproduced with yarn 1)

Logs

[vite] connecting...
Uncaught (in promise) TypeError: __rolldown_runtime__.requestLazy is not a function
    at http://localhost:5173/assets/index.js:58:42
[vite] connected.

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