fix(build): resolve non-hoisted SWC helpers

[NathanDrake2406]

Overview

Field	Details
goal	Match Next.js when server-side page code requires @swc/helpers without an app-root helper install.
core change	Add a Vite alias for @swc/helpers/_ to a concrete installed helper package, including pnpm virtual-store layouts.
boundary	Pages Router production build and deploy-suite fixtures that do not hoist SWC helpers.
primary files	packages/vinext/src/index.ts, tests/pages-router.test.ts, scripts/e2e-deploy.sh
expected impact	Existing Next.js apps no longer need @swc/helpers visible from their root node_modules for server page builds.

Why

Next.js treats SWC helpers as framework-owned build/runtime helpers, not app-root dependencies. Its server externalization explicitly keeps @swc/helpers bundled, and its compiler aliases @swc/helpers/_ to an installed helper copy. Vinext already bundles server deps, but without the alias Vite/Rolldown resolved require('@swc/helpers/_/_object_spread') from the page file and failed when the helper was not hoisted.

Area	Principle / invariant	What this PR changes
Server module resolution	Framework helpers should not require app-root hoisting.	Resolves the helper package from direct app installs, nested Next installs, pnpm virtual-store installs, or vinext context.
Next.js parity	Preserve upstream observable behaviour.	Ports the upstream handle-non-hoisted-swc-helpers Pages Router fixture into vinext coverage.
Deploy-suite adapter	The custom adapter owns throwaway fixture installation.	Removes non-pnpm packageManager metadata in temp apps and calls the linked vinext binary directly after install.

What changed

Scenario	Before	After
getServerSideProps requires @swc/helpers/_/_object_spread and helpers are not app-hoisted	Production build fails during module resolution.	Build succeeds and the page renders hello world.
Upstream npm-specific deploy fixture under vinext deploy adapter	pnpm refuses the fixture packageManager, or pnpm exec rechecks deps after init mutations.	Adapter install proceeds and the upstream file reaches the original assertion.

Maintainer review path

1. packages/vinext/src/index.ts: review resolveSwcHelpersUnderscoreDir() and the @swc/helpers/_ alias wiring.
2. tests/pages-router.test.ts: review the ported fixture and assertion against the upstream Pages Router test.
3. scripts/e2e-deploy.sh: review the temp manifest package-manager normalization and direct node_modules/.bin/vinext calls.

Validation

• vp test run tests/pages-router.test.ts -t "non-hoisted SWC helpers"
• vp env exec --node 24 ./scripts/run-nextjs-deploy-suite.sh /Users/nathan/Projects/vinext/.refs/nextjs-v16.2.6 --retries 0 -c 1 --debug test/e2e/handle-non-hoisted-swc-helpers/index.test.ts
• vp fmt --check packages/vinext/src/index.ts tests/pages-router.test.ts
• vp check packages/vinext/src/index.ts tests/pages-router.test.ts
• bash -n scripts/e2e-deploy.sh
• pre-commit hook: vp check --fix, full check, staged unit/integration tests, knip

Risk / compatibility

• Public API: none.
• Runtime: only affects resolving @swc/helpers/_... specifiers that would otherwise fail or depend on hoisting.
• Package managers: supports npm-style direct/nested installs and pnpm virtual-store installs.
• Deploy-suite: package-manager normalization is limited to throwaway Next.js test apps created by the custom adapter.

References

Reference	Why it matters
Next.js upstream test	Defines the expected observable behaviour.
Next.js server externalization	Shows @swc/helpers should not be externalized because hoisting cannot be relied on.
Next.js compiler alias	Shows the @swc/helpers/_ alias this PR mirrors for Vite.

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commit: f791f43