Resolves to the active error-reveal trigger for the surrounding
CngxFormField - the showErrors flag the presenter ORs into its error
gate, so a form can reveal every field's errors at once (typically on a
failed submit) rather than waiting for each to be touched.
Producers:
CngxErrorScopeFieldBridge (default) - bridges the nearest CngxErrorScope.
router-, interceptor-, or test-driven triggers - supply their own
CngxFormFieldRevealContract instead.
Optional. With no provider the presenter falls back to the
touched OR strategy(...) gate and the reveal channel is simply absent.