chore: remove Breadcrumbs component feature flag

[totally-not-ai]

The Breadcrumbs component is no longer experimental, so the feature flag that gated it and all of its plumbing can go away. Previously, attaching a Breadcrumbs to a UI without com.vaadin.experimental.breadcrumbsComponent=true threw at attach time; now the component just works out of the box.

What changed

• Breadcrumbs: dropped the checkFeatureFlag(UI) call from onAttach along with the private helper and the FeatureFlags import; removed the "this component is experimental" paragraph from the class Javadoc.
• Removed BreadcrumbsFeatureFlagProvider and its META-INF/services/com.vaadin.experimental.FeatureFlagProvider registration, so the flag no longer shows up in the experimental features list.
• Removed ExperimentalFeatureException, which existed only to report the disabled flag.
• Tests: deleted FeatureFlagTest (it only covered enabled/disabled attach behaviour) and dropped the EnableFeatureFlagExtension registration from BreadcrumbsModeTest, which now exercises the component the way an application will.
• Integration tests: deleted vaadin-featureflags.properties, which only contained the breadcrumbs flag entry.

No references to the flag, provider, or exception remain in the repository.

API Changes

com.vaadin.flow.component.breadcrumbs.BreadcrumbsFeatureFlagProvider

// Removed
public class BreadcrumbsFeatureFlagProvider implements FeatureFlagProvider
public BreadcrumbsFeatureFlagProvider()
public static final Feature BREADCRUMBS_COMPONENT
public List<Feature> getFeatures()

com.vaadin.flow.component.breadcrumbs.ExperimentalFeatureException

// Removed
public class ExperimentalFeatureException extends RuntimeException
public ExperimentalFeatureException() // no longer thrown; Breadcrumbs is not gated

Test summary

#	Status	What the test verifies	Why it matters
1	✅	A Breadcrumbs can be added to a UI with no feature flag configured and attaches without throwing	This is the whole point of the change — a leftover flag check would break every application on attach
2	✅	Router mode still registers exactly one AfterNavigationListener on attach, and manual mode registers none, with no flag enabled	onAttach was edited; the listener wiring must survive removal of the flag check
3	✅	Router mode still builds the trail from the route hierarchy (static, dynamic and query-parameter titles) after attach	Guards against the attach path regressing while the flag check was stripped out
4	✅	Detach still unregisters the navigation listener, and setMode switching on an attached instance rewires listeners/children	Attach/detach lifecycle is the code path that was touched

Tests changed on this branch (no new test methods were added — this change only removes behaviour):

• BreadcrumbsModeTest — the EnableFeatureFlagExtension registration was removed, so every existing test in the class now runs against an unflagged environment. BreadcrumbsModeTest.routerMode_attach_registersExactlyOneAfterNavigationListener and BreadcrumbsModeTest.manualMode_attach_doesNotRegisterListener cover rows 1 and 2; BreadcrumbsModeTest.routerMode_afterNavigationEvent_buildsTrailFromRouteHierarchy, BreadcrumbsModeTest.routerMode_currentViewHasDynamicTitle_usedForLastItem, BreadcrumbsModeTest.routerMode_currentItemTitle_resolvedWithQueryParameters and BreadcrumbsModeTest.routerMode_ancestorTitle_resolvedWithoutQueryParameters cover rows 1 and 3; BreadcrumbsModeTest.routerMode_detach_unregistersListener, BreadcrumbsModeTest.setModeRouter_onAttachedManualInstance_registersListenerAndBuildsTrail and BreadcrumbsModeTest.setModeManual_onAttachedRouterInstance_unregistersListenerAndClearsTrail cover row 4.
• FeatureFlagTest.featureEnabled_attach_doesNotThrow / FeatureFlagTest.featureDisabled_attach_throws — deleted; both asserted behaviour that no longer exists.

Deliberately untested: that BreadcrumbsFeatureFlagProvider is gone from the FeatureFlagProvider service registry and that the flag no longer appears in Copilot's experimental features tab — both are absence-of-a-file facts with nothing left to assert against, verified by grep instead.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud