[next-rspack] NextExternalsPlugin wrongly externalizes transpilePackages direct dependencies on Windows + pnpm (dev only, pages router) #98505

Link to the code that reproduces this issue

https://github.com/helloworldcyj/rspack-next-externals-repro

To Reproduce

One-time setup: generates vendor/demo-service-1.0.0.tgz from packages/service
(the tarball is NOT committed to git), then installs dependencies
pnpm bootstrap

① rspack dev (bug scene)
pnpm repro:rspack
Open http://localhost:3100
The page shows: SSR resolve result: FAILED: No matching bindings found for serviceIdentifier: Symbol(Config)

② webpack dev (control group, behaves correctly)
pnpm repro:webpack
The page shows: SSR resolve result: OK, answer = 42

③ rspack production build (also works fine, which shows the issue is dev-mode specific)
pnpm build:rspack

Current vs. Expected behavior

Environment: Windows + pnpm (junctions inside node_modules) + Next.js 16.3.0 + next-rspack 16.3.0 (NEXT_RSPACK=true) + pages router
Expected: both transpile packages are bundled into the pages router server bundle (this is what happens in webpack mode)

Provide environment information

Environment: Windows + pnpm (junctions inside node_modules) + Next.js 16.3.0 + next-rspack 16.3.0 (NEXT_RSPACK=true) + pages router

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

Runtime

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

next dev (local)

Additional context

No response