[morinokami]

When an app's package.json declares "sideEffects": false, a production build leaves env.ts out of the Worker, so env from void/env returns raw values:

// env.ts
import { boolean, defineEnv, number } from 'void/env';

export default defineEnv({
  PORT: number().default(3000),
  DEBUG: boolean(),
});

With DEBUG=false and no PORT in the Worker's env, env.PORT is undefined and env.DEBUG is the string "false", so if (env.DEBUG) takes the debug branch. No schema is registered, so the boot validation passes any value, and a missing required key goes unnoticed. vp dev doesn't bundle, so it reads validated values, and the difference only shows after a build.

The generated entry imports env.ts only for its side effect, registering the schema, and uses none of its exports. The bundler follows the app's sideEffects field and drops the import. An array that doesn't match env.ts, such as ["**/*.css"], drops it too. An app whose code imports the env that env.ts exports keeps it.

The field is uncommon in apps, but some starters set it: most of TanStack Start's official examples declare "sideEffects": false.

Fix

In server builds, envSchemaPlugin returns moduleSideEffects: true for env.ts from a transform hook. Rolldown uses this value over the package's sideEffects field.

• The hook matches the env file's path as found and as Vite resolves it, so a symlinked env.ts is covered whatever its target is named.
• Client builds are unchanged. The browser variant of void/env reads import.meta.env and doesn't use the schema.

Tests

packages/void/test/integration/plugin-env-schema.test.ts builds an entry that imports env.ts for its side effect, in an app that declares "sideEffects": false:

• A server build keeps env.ts, also when env.ts is a symlink to a file with another name. Both cases fail without this fix.
• A client build still leaves it out.

Verification

• vp test run: 781 files pass, 1 skipped (16,170 tests pass, 29 skipped).
• vp run check: 33/33 pass.
• By hand on a copy of playground/ssr with the env.ts above, "sideEffects": false, DEBUG=false in .env, and a route that returns both values: in vp preview, the route reads PORT as 3000 and DEBUG as false. Without this fix, the Worker bundle has no env.ts, and the route reads undefined and "false". vp dev reads the validated values without this fix too.
• By hand with ["**/*.css"] instead: an app built with envSchemaPlugin and an entry that imports env.ts for its side effect drops env.ts without this fix and keeps it with it.
• Not run: void deploy against Cloudflare.

🤖 Generated with Claude Code