[RafalOfficial]

Problem

On Windows, the unit suite fails from a checkout without built dist directories. ensureBuilt (the test helper in packages/client and packages/server) runs pnpm build with execFile. On Windows pnpm is a pnpm.cmd shim, and execFile can only start that through a shell, so the build never runs:

FAIL  test/client/coreBoundary.test.ts > @modelcontextprotocol/client ↔ core schema boundary
Error: pnpm build failed in ...\packages\core: spawn pnpm ENOENT
 ❯ ensureBuilt test/helpers/ensureBuilt.ts:103:27

Every suite that needs a built dist fails this way (client: barrelClean, coreBoundary, workerdSchemaPreload; server: barrelClean, workerdSchemaPreload). With pnpm -r test the client failure also stops the run before the middleware and integration packages are tested. CI runs on Ubuntu only, so it does not see this.

Fix

Pass shell: process.platform === 'win32' to the execFile call in both helpers. Nothing changes on other platforms. Test code only, so no changeset.

Testing

Windows 11, Node 24.16.0, pnpm 10.26.1, with this commit applied on current main (919bb8e), after deleting every packages/*/dist. The branch itself is based on the older 9bc40e9; neither helper has changed since, and it merges cleanly:

• Before: pnpm --filter @modelcontextprotocol/client test → 3 files fail with spawn pnpm ENOENT.
• After: pnpm -r --filter '!@modelcontextprotocol/test-e2e' test (the CI command) → all packages pass (client 44 files / 1078 tests, server 55 files / 672 tests).
• pnpm --filter @modelcontextprotocol/client --filter @modelcontextprotocol/server lint and typecheck → clean.

One side effect, on Windows only: Node 24 prints the DEP0190 warning (args passed together with shell: true) when the helper has to build. The arguments are the constant ['build']. I did not test on Linux or macOS; the option is false there.

AI disclosure

This change was found, written and tested with Claude Code (an AI coding agent) running on a Windows machine.

🤖 Generated with Claude Code

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commit: d325961