`vp test` doesn't pick up loader configuration for `vp pack`

[gBasil]

Describe the bug

I have a basic package that imports a .txt file as text (pack: { loader: { ".txt": "text" } }) that I build with vp pack. It successfully builds, as expected, but when trying to run tests with vp test, the file does not get imported properly, and instead of returning the text file, the .txt import returns the file path from the project root.

Reproduction

https://github.com/gBasil/vp-test-loader-repro

Steps to reproduce

vp install

# Observe that the package builds properly:
vp pack

# Observe that it fails
vp test

System Info

VITE+ - The Unified Toolchain for the Web

Environment:
  Version  24.18.0
  Source   lts

Tool Paths:
  node  /Users/basil/.vite-plus/js_runtime/node/24.18.0/bin/node
  npm   /Users/basil/.vite-plus/js_runtime/node/24.18.0/bin/npm
  npx   /Users/basil/.vite-plus/js_runtime/node/24.18.0/bin/npx

Package Manager:
  Name          pnpm
  Version       11.13.0
  Source        devEngines.packageManager
  Source Path   /Users/basil/Downloads/vp-error/package.json
  Project Root  /Users/basil/Downloads/vp-error
  Bin Path      /Users/basil/.vite-plus/package_manager/pnpm/11.13.0/pnpm/bin/pnpm

---

VITE+ - The Unified Toolchain for the Web

vp v0.2.4

Local vite-plus:
  vite-plus  v0.2.4

Tools:
  vite             v8.1.3
  rolldown         v1.1.4
  vitest           v4.1.10
  oxfmt            v0.57.0
  oxlint           v1.72.0
  oxlint-tsgolint  v0.24.0
  tsdown           v0.22.3

Environment:
  Package manager  pnpm v11.13.0
  Node.js          v24.18.0

Used Package Manager

pnpm

Logs

Validations

• Read the Contributing Guidelines.
• Check that there isn't already an issue for the same bug.
• Confirm this is a Vite+ issue and not an upstream issue (Vite, Vitest, tsdown, Rolldown, or Oxc).
• The provided reproduction is a minimal reproducible example.