MSW fails to import when running unit tests in browser mode

[prowe]

Which @angular/* package(s) are the source of the bug?

compiler

Is this a regression?

Yes

Description

In Angular 21, when running unit tests using the below configuration the run fails with "The entry point "msw" cannot be marked as external"

Setup:

1. Create a new angular project.
2. Set unit tests to use the chromium browser
3. Install MSW
4. Attempt to import anything from msw in a test case, the above error is thrown.

This appears to be related to a disconnect between the package.json configuration of MSW and the "resolve conditions" that are being passed to Vitest by the angular unit test runner.

When running the tests in jsdom (not browser) we do not encounter this issue.

Please provide a link to a minimal reproduction of the bug

No response

Please provide the exception or error you saw

Please provide the environment you discovered this bug in (run ng version)

Angular CLI       : 21.1.4
Angular           : 21.1.5
Node.js           : 22.18.0
Package Manager   : npm 11.5.2
Operating System  : win32 x64

┌───────────────────────────┬───────────────────┬───────────────────┐
│ Package                   │ Installed Version │ Requested Version │
├───────────────────────────┼───────────────────┼───────────────────┤
│ @angular/build            │ 21.1.4            │ ^21.1.4           │
│ @angular/cli              │ 21.1.4            │ ^21.1.4           │
│ @angular/common           │ 21.1.5            │ ^21.1.0           │
│ @angular/compiler         │ 21.1.5            │ ^21.1.0           │
│ @angular/compiler-cli     │ 21.1.5            │ ^21.1.0           │
│ @angular/core             │ 21.1.5            │ ^21.1.0           │
│ @angular/forms            │ 21.1.5            │ ^21.1.0           │
│ @angular/platform-browser │ 21.1.5            │ ^21.1.0           │
│ @angular/router           │ 21.1.5            │ ^21.1.0           │
│ rxjs                      │ 7.8.2             │ ~7.8.0            │
│ typescript                │ 5.9.3             │ ~5.9.2            │
│ vitest                    │ 4.0.18            │ ^4.0.8            │
└───────────────────────────┴───────────────────┴───────────────────┘

Anything else?

No response