Turbopack: WASM fetch URLs return 404 on Vercel due to double-encoded deployment suffix

[johnzook]

Link to the code that reproduces this issue

https://github.com/zookanalytics/vercel_wasm

To Reproduce

1. Clone https://github.com/zookanalytics/vercel_wasm
2. Deploy to Vercel (or see live deployment below)
3. Open browser DevTools → Network tab
4. Observe: .wasm request with %3Fdpl%3D in the path returns 404

Live deployment: https://vercelwasm.vercel.app/

It works fine running locally on dev, only manifests when deployed via Vercel as it adds the ?dpl suffix

Current vs. Expected behavior

Expected: WASM loads from /_next/static/chunks/xxx.wasm?dpl=dpl_xxx (200)

Actual: Browser requests /_next/static/chunks/xxx.wasm%3Fdpl%3Ddpl_xxx?dpl=dpl_xxx (404). The deployment suffix appears twice — once URL-encoded into the path, once as a proper query parameter.

Provide environment information

Operating System:
  Platform: linux
  Arch: arm64
  Version: #1 SMP PREEMPT Thu Nov 20 09:34:02 UTC 2025
  Available memory (MB): 32103
  Available CPU cores: 10
Binaries:
  Node: 22.22.2
  npm: 10.9.7
  Yarn: 1.22.22
  pnpm: 10.33.0
Relevant Packages:
  next: 16.2.2 // Latest available version is detected (16.2.2).
  eslint-config-next: N/A
  react: 19.2.4
  react-dom: 19.2.4
  typescript: 6.0.2
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Turbopack

Which stage(s) are affected? (Select all that apply)

Vercel (Deployed)

Additional context

Affected versions: 16.2.0, 16.2.1, 16.2.2. Works in 16.1.7.

Note: This is the same bug reported in #91778, which was auto-closed for lacking a reproduction link.

Likely Root cause:

In the Turbopack runtime (turbopack-*.js), WASM chunk paths go through two steps that both add the ?dpl= suffix:

1. .q() appends the suffix when registering the module: "static/chunks/xxx.wasm" → "static/chunks/xxx.wasm?dpl=xxx"
2. loadWebAssembly passes that path to N(), which encodeURIComponent's each /-separated segment (encoding the ? already in it to %3F), then appends the suffix again.

JS and CSS chunks don't hit this because they load via <script>/ tags, not fetch(). In Next.js 16.1.7, the equivalent function .v() stored paths without the suffix, so N() correctly appended it only once.