fix(vite): rebuild component styles when a transitive preprocessor dependency changes

[Alexays]

Problem

Editing a stylesheet that a component style depends on transitively (a Sass partial pulled in through @use / @import / meta.load-css, a Less import, ...) does nothing in dev mode: the compiled component style is cached and no HMR update is dispatched. The stale CSS is served until the styleUrl file itself is touched (or the dev server restarted).

The Angular CLI's builder handles this case (it watches the Sass loadedUrls), so projects migrating to this plugin lose partial watching silently, which is easy to misdiagnose as an application bug. In our app the shared partial is included by a dozen component stylesheets, and edits to it were invisible.

Root cause

resolveResources runs each styleUrl through Vite's preprocessCSS, which already reports every file the preprocessor loaded in processed.deps, but the plugin discarded that field. Transitive deps were therefore never registered in resourceToComponent, so handleHotUpdate fell through to Vite's default pipeline (which has no module for them either), and the resourceCache entry for the compiled style was never invalidated.

Fix

• Capture processed.deps (normalized) per compiled style, cached alongside the compiled CSS so cache hits re-register them and the transform's prune loop does not drop them.
• Keep a reverse map from each dep to every style compiled on top of it. This has to be multi-owner: resourceToComponent keeps a single owner per resource, and a shared partial belongs to many components; with a single owner only the last transformed component would receive the update.
• In handleHotUpdate, when a changed file is a known style dep: drop the compiled-CSS cache of every owning style and dispatch component HMR for each owner (the @ng/component endpoint already re-reads and re-preprocesses styles from disk, so the served update is fresh).

Tests

New style-deps-hmr.test.ts, reusing the harness style of hmr-hot-update.test.ts with a real resolved config so Sass actually runs and reports its deps:

• a change to a partial shared by two components dispatches angular:component-update for both and returns [];
• an untracked stylesheet still falls through to Vite (ctx.modules).

Adds sass as a devDependency for that test. pnpm test: 202 passed (12 files). oxfmt --check clean; the oxlint --type-aware failure on e2e/app/vite.config.ts is pre-existing on main.

Also validated end-to-end against a real application (large Angular admin, Sass partial shared by ~10 components): before the patch edits to the partial were never picked up; with it, each edit recompiles the owning styles and hot-updates every owning component within a couple of seconds.

[Brooooooklyn]

Do we really need this?