[georgylobko]

Description

Adds a feature flag that hides breadcrumbs in the AppLayout toolbar from the first render. This PR made it possible for an external consumer to take over breadcrumbs, and AppLayout then hides its own toolbar breadcrumbs. The consumer registers through an async event, though, so the breadcrumbs only get hidden after the first render, which causes a visible flicker. With this flag on, the toolbar breadcrumbs never render, so the flicker goes away.

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.70%. Comparing base (66cba18) to head (8e51f6a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5113   +/-   ##
=======================================
  Coverage   97.70%   97.70%           
=======================================
  Files         990      990           
  Lines       31818    31820    +2     
  Branches    11753    11753           
=======================================
+ Hits        31089    31091    +2     
- Misses        683      722   +39     
+ Partials       46        7   -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.

[Copilot]

Copilot review overview

🟡 Changes recommended

Renaming the cross-version widget state key without a compatibility fallback can restore duplicate toolbar breadcrumbs in mixed-version deployments.

Review effort: Balanced
Findings: 2

Open (2)

• Preserve legacy breadcrumb state key for cross-version compatibility · New
• Fallback to legacy breadcrumb key to prevent duplicate breadcrumbs · New

What changed in this PR

Adds a global feature flag to hide AppLayout toolbar breadcrumbs from the first render, preventing flicker before an external consumer registers.

Changes:

• Adds and propagates appLayoutHideToolbarBreadcrumbs.
• Renames the widgetized visibility state.
• Adds flag behavior tests and updates contract snapshots.

File	Description
src/​app-layout/​visual-refresh-toolbar/​widget-areas/​before-main-slot.tsx	Passes breadcrumb visibility state to the toolbar.
src/​app-layout/​visual-refresh-toolbar/​toolbar/​index.tsx	Adopts the renamed toolbar property.
src/​app-layout/​visual-refresh-toolbar/​state/​use-app-layout.tsx	Combines consumer registration with the global flag.
src/​app-layout/​visual-refresh-toolbar/​skeleton/​toolbar-container.tsx	Hides breadcrumbs based on the new state.
src/​app-layout/​visual-refresh-toolbar/​interfaces.ts	Updates the widgetized state interface.
src/​app-layout/​utils/​feature-flags.ts	Reads the new global flag.
src/​app-layout/​__tests__/​runtime-breadcrumbs-widgetized.test.tsx	Tests flagged breadcrumb behavior.
src/​app-layout/​__tests__/​__snapshots__/​widget-contract-split-panel-old.test.tsx.snap	Updates split-panel widget contracts.
src/​app-layout/​__tests__/​__snapshots__/​widget-contract-old.test.tsx.snap	Updates widget contract snapshots.
pages/​app/​index.tsx	Exposes the flag through development-page query parameters.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.