createMatTabHandle

Description#

Translates a Material MatTab into a cngx CngxTabHandle plus a writable errorAggregator slot the [cngxMatTabError] directive binds.

• id - fresh idSeed() value; a label-keyed id would collide when two tabs share a label.
• label / disabled - computed signals retriggered by toSignal(matTab._stateChanges). Bridge lifetime is tied to the supplied injector (typically a per-tab child EnvironmentInjector). _stateChanges is a Material-internal surface.
• errorAggregator - writable seeded at undefined; [cngxMatTabError] writes its bound aggregator in and resets on teardown. The handle exposes .asReadonly() to preserve the CngxTabHandle contract.
• directError - writable seeded at false; [cngxMatTabErrorFlag] writes its string | boolean value in and resets on teardown. Folds into hasError / errorMessage.