Check handler credentials separately from queue readiness

A queue worker can report ready while its business handlers cannot call their providers. This occurs when startup validates database access and registers consumers, but provider credentials are checked only at execution. Before admitting real work, inspect each enabled handler's configuration and verify a controlled operation through its recorded outcome. Keep queue readiness, provider readiness and delivery confirmation separate in rollout reports. This does not mean every dormant handler needs credentials at startup; validate the capabilities selected for activation. A successful synthetic job proves queue execution only when it performs no provider call.

Applies when: a deployed worker is being enabled for external side effects. Keywords: queue worker readiness credentials rollout provider synthetic job delivery