feat: Publish breadcrumbs through widget API

[ajsuvarna6]

Description

Adds a widget API for rendering App Layout breadcrumbs in Global Navigation or another external container, without requiring console teams to adopt App Layout bundle changes before the consumer can register.

registerBreadcrumbsConsumer handles external ownership only. App Layout stores the registered consumer callback in a ref and uses a boolean as the single source of truth for whether breadcrumbs are externally owned. Registration sets ownership, and the returned unregister closure clears that registration and restores toolbar rendering. Only one external consumer can be registered at a time.

Own-breadcrumb extraction is kept separate from external consumer registration. The internal extractOwnBreadcrumbs callback captures the complete BreadcrumbGroupProps from the widgetized BreadcrumbGroup rendered in the App Layout slot, including through console wrapper components. App Layout then reconciles own and discovered breadcrumbs in one place using the existing source priority.

A layout effect publishes the resolved breadcrumb props, or null, to the active external consumer whenever they change. Publishing is visibility-aware: a mounted App Layout that becomes hidden publishes null, preventing it from leaving stale breadcrumbs or overriding a visible App Layout.

While breadcrumbs are externally owned, App Layout keeps its BreadcrumbGroup and funnel analytics markers in the DOM but hides the toolbar breadcrumb section with display: none. Unregistering the consumer makes the toolbar breadcrumbs visible again.

There is no startup global flag or pre-registration reservation. Ownership begins when the external consumer registers. The demos exercise the late-mount order where App Layout renders first and the Global Navigation consumer registers afterward.

Related links, issue #, if available: #4984

How has this been tested?

• Added 14 unit tests covering consumer registration and cleanup, own and discovered breadcrumbs, prop and handler updates, wrapper components, source reconciliation, duplicate consumers, analytics markers, and visibility behavior.
• Added 6 browser integration tests covering late consumer registration, producer updates, multiple App Layouts, separate iframe roots, hidden mounted layouts, and restoration after consumer removal.
• Added development demos for:
  • app-layout/global-nav-breadcrumbs
  • app-layout/global-nav-breadcrumbs-multi-layout
  • app-layout/global-nav-breadcrumbs-multi-instance
  • app-layout/global-nav-breadcrumbs-hidden-instances-iframe
• Changed-file lint passed.
• npm run quick-build passed.
• Production npm run build passed.
• Production size limits passed.

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?

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[georgylobko]

Overall, the PR involves solving a few separate problems:

Accessing the currently rendered breadcrumb group

1. Establish communication between breadcrumb-group/implementation and use-app-layout so that use-app-layout can access the breadcrumb props.
2. We already have access to discoveredProps.
3. We know that the component’s own breadcrumb props should take precedence.

Once we determine which breadcrumb instance is being rendered external or internal, we will have access to its props.

External communication

We need to declare an event in plugins/widget, subscribe to it in useWidgetMessages, listen for it, and trigger it with the reconciled props.

Deciding whether to render breadcrumbs in the AppLayout toolbar

After completing the previous steps, we will know whether there is an external consumer. At that point, we can decide whether to hide the breadcrumbs in the toolbar.

Let’s keep these steps separate and avoid mixing them together

[georgylobko]

Approving the PR with few optional comments, you can address them in a follow-up

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.80%. Comparing base (3fb837b) to head (1e286e4).

Additional details and impacted files

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##             main    #5005      +/-   ##
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- Coverage   97.68%   93.80%   -3.89%     
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  Files         965      965              
  Lines       31484    27306    -4178     
  Branches    11641     9824    -1817     
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- Hits        30755    25614    -5141     
+ Misses        683      611      -72     
- Partials       46     1081    +1035     

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