Backport fix #33525 to Angular 21

[leo2823]

Command

serve

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

I would like to request a backport of #33525 to the Angular 21 branch.
The issue affects ng serve --configuration=production when externalDependencies are used and the generated code is optimized/minified. The angular-plugin-remove-id-prefix Vite plugin currently uses a greedy regex:

(?:/.+)?

When the generated code is minified into a single line and an external dependency has a deep import path (for example @angular/common/http), the regex can consume the remainder of the line. As a result, subsequent /@id/ prefixes are not stripped.
The browser then requests URLs such as:

/@id/@angular/router

The Angular dev server responds with the application's index.html fallback, resulting in:

Error: Unsupported Content-Type "text/html" loading http://localhost:4200/@id/@angular/core

The issue has already been fixed upstream changing the regular expression in:

#33525

Importantly, the PR explicitly states that the fix was verified end-to-end with @angular/build 21.2.0 by applying the change directly to node_modules in a real application.

Minimal Reproduction

A complete minimal reproduction is already available in the original issue:

• Issue dev-server: /@id/ prefix not stripped from minified bundles when using externalDependencies (greedy regex in createRemoveIdPrefixPlugin) #33524:

• Fix: PR #33525

Exception or Error

Error: Unsupported Content-Type "text/html" loading http://localhost:4200/@id/@angular/core

Your Environment

Angular CLI       : 21.2.24
Angular           : 21.2.23
Node.js           : 24.16.0
Package Manager   : npm 11.13.0
Operating System  : win32 x64

┌───────────────────────────────────┬───────────────────┬───────────────────┐
│ Package                           │ Installed Version │ Requested Version │
├───────────────────────────────────┼───────────────────┼───────────────────┤
│ @angular/build                    │ 21.2.24           │ ~21.2.11          │
│ @angular/cdk                      │ 21.2.14           │ ~21.2.11          │
│ @angular/cli                      │ 21.2.24           │ ~21.2.11          │
│ @angular/common                   │ 21.2.23           │ ~21.2.11          │
│ @angular/compiler                 │ 21.2.23           │ ~21.2.11          │
│ @angular/compiler-cli             │ 21.2.23           │ ~21.2.11          │
│ @angular/core                     │ 21.2.23           │ ~21.2.11          │
│ @angular/forms                    │ 21.2.23           │ ~21.2.11          │
│ @angular/platform-browser         │ 21.2.23           │ ~21.2.11          │
│ @angular/router                   │ 21.2.23           │ ~21.2.11          │
│ ng-packagr                        │ 21.2.7            │ ^21.0.0           │
│ rxjs                              │ 7.8.2             │ ~7.8.2            │
│ typescript                        │ 5.9.3             │ ~5.9.0            │
│ zone.js                           │ 0.16.3            │ ~0.16.2           │
└───────────────────────────────────┴───────────────────┴───────────────────┘

Anything else relevant?

No response

[alan-agius4]

Version 21 is currently in Long-Term Support (LTS) and receives only security-related updates. Because this is not a security issue, it does not qualify for a backport.