[BUG] Turbopack ignores `workerd` export condition for `@react-email/render`

[zammitjohn]

Description

When using resend with React email templates on Cloudflare Workers via OpenNext, sending emails fails at runtime with:

Failed to render React component. Make sure to install `@react-email/render` or `@react-email/components`.

@react-email/render is installed. This worked on Next.js 15 (webpack) and broke on Next.js 16 (Turbopack).

Root Cause

@react-email/render provides conditional exports in its package.json:

• workerd → dist/edge/index.mjs (uses WritableStream — works on Workers)
• node → dist/node/index.mjs (uses node:stream — fails on Workers)

Turbopack always picks the node entry. The resulting chunk is named node_modules_@react-email_render_dist_node_index_mjs_*.js and contains require("node:stream").

OpenNext's esbuild runs after Turbopack with conditions: ["workerd"], but Turbopack has already resolved the wrong entry. The workerd condition never gets a chance.

Webpack (Next.js 15) correctly resolved to the edge-compatible build with WritableStream and zero node:stream references.

Reproduction

https://github.com/zammitjohn/resend-cloudflare-repro

git clone https://github.com/zammitjohn/resend-cloudflare-repro.git
cd resend-cloudflare-repro
npm install
npm run preview
# Click "Send Test Email" → fails

Verify the wrong resolution

npx opennextjs-cloudflare build

# Turbopack chose the node entry:
ls .open-next/server-functions/default/.next/server/chunks/ssr/ | grep react-email
# → node_modules_@react-email_render_dist_node_index_mjs_*.js

# The chunk requires node:stream:
grep 'require("node:stream")' .open-next/server-functions/default/.next/server/chunks/ssr/\[root-of-the-server\]__*.js

Versions

Package	Broken (Turbopack)	Working (webpack)
next	16.1.5	15.5.9
@opennextjs/cloudflare	^1.17.1	^1.14.4
resend	^6.10.0	^6.6.0
@react-email/render	^2.0.6	^2.0.0