library builder: in watch mode, editing a Sass partial doesn't re-emit components that import it via @use #34124

Command

build

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

Found while tesing #34106 cc @alan-agius4

In --watch changing a partial that component stylesheet reaches through @use logs a successful rebuild, but component's CSS in FESM stays old. Editing component's own .scss or .html works (what watch_spec covers)

Non watch builds are fine

Minimal Reproduction

1. widget.scss: @use './styles/shared' as s; .my-widget { @include s.paint; };
2. _shared.scss: @mixin paint { color: rgb(1,1,1); }
3. ng build mylib --watch then change mixin to rgb(2,2,2);
4. rebuild logs success, FESM still has #010101. Touching widget.ts flushes it and #020202 appears

Exception or Error

Your Environment

@angular/build built from #34106 (e1fa5796) with the repo's own bazel build

Angular CLI 22.1.8, 
Angular 22.1.7, 
Node 24.16.0, 
pnpm 11, 
macOS 25.6, 
14 cores, 
24 GB

Anything else relevant?

sass itself is re-bundled correctly. component never enters affectedFiles because only the direct styleUrl is a known resource dependency. application builder expands modified files with FileReferenceTracker (compiler-plugin.ts); the library pipeline doesn't use it.

On ngwr every component stylesheet @uses the theme partials, so any token or mixin edit in watch is stale.