Regression in 5.109.0: resolve.alias mapping to an absolute path that points at a package directory no longer resolves #21541

Have you used AI?

Yes

Bug Description

Using resolve.alias to make an alias to an absolute path of a package inside node_modules, webpack 5.109.0+ fails to resolve the package with the following error:

Module not found: Error: Can't resolve 'vendor/tippy.js'

This worked in 5.108.4

Link to Minimal Reproduction and step to reproduce

// webpack.config.js
const path = require('path');
module.exports = {
  mode: 'development',
  entry: './index.js',
  resolve: {
    alias: { vendor: path.resolve(__dirname, 'node_modules') },
  },
};

// index.js
import('vendor/tippy.js');

Build with webpack 5.109.0/5.109.1 → can't resolve 'vendor/tippy.js' error
Build with webpack 5.108.4 → succeeds

Expected Behavior

vendor/tippy.js should resolve using the configured alias to <abs>/node_modules/tippy.js as it did in 5.108.4

Actual Behavior

Can't resolve error

Environment

- Webpack: first-bad at 5.109.0 (also bad at 5.109.1); last-good 5.108.4
- enhanced-resolve: 5.24.3 (identical on both)
- Node.js: v24.18.0 and v26.5.0
- OS: macOS (darwin)
- verified by installing 5.108.4 / 5.109.0 / 5.109.1 side-by-side and running the same config + entry against each

Is this a regression?

Yes (please specify version below)

Last Working Version

5.108.4

Additional Context

Investigated with the help of claude, reviewed humanly before posting