Implement CpsRootFontSizeService

[fateeand]

Overview

Implemented CpsRootFontSizeService that tracks the application's current root font size.
The service uses a ResizeObserver strategy to reliably detect root font-size changes on a sentinel element (<div style="width:1rem;height:0">).
Its pixel width mirrors 1rem. Any root font-size change caused by CSS class toggles, stylesheet rules, direct JS assignment, or viewport resize (e.g. font-size: 1.5vw) changes the sentinel's computed width, firing the observer.
The cached value is stored in a signal and is only updated when the actual font-size value changes, preventing spurious updates.

In microfrontend environments the sentinel element is keyed by a known DOM attribute (data-cps-root-font-size-sentinel) and reused if already present, so only one sentinel node exists per document regardless of how many instances of this service are created. The sentinel is intentionally never removed from the DOM - it is a lightweight, invisible element and removing it could silently break any other live service instance still observing it.

Only active in browser environments. Under SSR the fontSize signal is initialized to 16 (the standard browser default) and no DOM observers are created.

The injection token CPS_ROOT_FONT_SIZE_SERVICE for the root font size service is created. By default it resolves to the singleton CpsRootFontSizeService.

Consumer apps can override it to supply a custom subclass or to provide null to disable dynamic tracking entirely.
Injecting CPS_ROOT_FONT_SIZE_SERVICE in consumer apps should be preferred over injecting the service class directly, as it allows them to override the implementation behavior.

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Follow-up scope

• Work item to integrate the service into the library components: Integrate CpsRootFontSizeService into components #583
• Work item to showcase the service API in the composition app: Create a Services group in the composition app #582

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Release notes:

• Implement CpsRootFontSizeService

[github-actions]

Coverage report for library

St.❔	Category	Percentage	Covered / Total
🔴	Statements	30.34%	2093/6899
🔴	Branches	24.1%	758/3145
🔴	Functions	26.44%	386/1460
🔴	Lines	31.11%	1974/6345

Test suite run success

473 tests passing in 23 suites.

Report generated by 🧪jest coverage report action from e0d735d

[Copilot]

Pull request overview

This PR introduces a new Angular service to track the current document root font size (rem baseline) at runtime, primarily to support components that need accurate px↔rem conversions across dynamic theme/layout changes and microfrontend setups.

Changes:

• Added CpsRootFontSizeService using a ResizeObserver on a shared “1rem” sentinel element to react to root font-size changes.
• Added Jest unit tests for browser/SSR behavior and for the CPS_ROOT_FONT_SIZE_SERVICE injection token.
• Updated the API generator to skip writing empty per-module JSON outputs.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
projects/cps-ui-kit/src/public-api.ts	Exports the new root font-size service from the library public surface.
projects/cps-ui-kit/src/lib/services/cps-root-font-size/cps-root-font-size.service.ts	Implements root font-size tracking + injection token for override/disable scenarios.
projects/cps-ui-kit/src/lib/services/cps-root-font-size/cps-root-font-size.service.spec.ts	Adds unit coverage for browser mode, SSR mode, sentinel reuse, and token resolution.
api-generator/api-generator.js	Skips emitting JSON files for empty docs modules.

[github-actions]

Playwright test results

 56 passed

Details

 56 tests across 4 suites
 1 minute, 43 seconds
 e0d735d
 For details, download the Playwright report