[vvaliyev]

Description

Adds the internal Style API v2 to Textarea with one slot, textarea, on the native <textarea> element, which is also the field box.

Tracker section: P3d34KdbCd6o.

How has this been tested?

• npm run build, unit tests for src/textarea and the style-docs snapshot, prettier, stylelint, eslint.
• New unit test src/textarea/__tests__/style-api.test.tsx: the slot class lands on the native textarea in every state, unknown keys are ignored, the prop does not reach the DOM, v1 inline styles still apply.
• New dev page pages/textarea/style-api-v2 styled only through the generated textarea.textarea() mixin, one permutation per row and per documented state; verified in the browser. No VR baseline yet (not registered in the VR suite, same as the other style-api-v2 pages).
• Console build CSS compared against main: only the three v1 fallback fixes differ.

[Copilot]

🟢 Approval recommended

The scoped implementation follows existing Style API patterns, with no unresolved correctness or compatibility findings.

No open issues 🎉

What changed in this PR

Adds internal Style API v2 support to Textarea through a single textarea slot on the native field element.

Changes:

• Adds slot class support, placeholder tokens, and generated styling documentation.
• Corrects three existing Style API v1 hover and focus fallbacks.
• Adds slot behavior tests, a documentation snapshot, and a styled demo page.

File	Description
src/​textarea/​styles.scss	Registers styling tokens and documentation; corrects v1 fallbacks.
src/​textarea/​index.tsx	Applies the internal slot class to the native textarea.
src/​textarea/​__tests__/​style-api.test.tsx	Tests slot placement, component states, and prop filtering.
src/​__tests__/​snapshot-tests/​__snapshots__/​style-docs.test.ts.snap	Adds Textarea styling documentation snapshots.
pages/​textarea/​style-api-v2.scss	Defines demo styles using the generated mixin.
pages/​textarea/​style-api-v2.page.tsx	Demonstrates styling across Textarea states.

_{Review effort: Balanced}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.73%. Comparing base (b3106e4) to head (c646ebf).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5191   +/-   ##
=======================================
  Coverage   97.73%   97.73%           
=======================================
  Files         996      996           
  Lines       32222    32224    +2     
  Branches    11909    11909           
=======================================
+ Hits        31493    31495    +2     
- Misses        684      723   +39     
+ Partials       45        6   -39     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.