Read an occurrence

Reads one retained occurrence from the PostgreSQL authority that owns its schedule. Trusted first-outbound timing is optional for records that predate substantiation; when present, firstAttemptLatenessMs is signed and a negative value exposes an early-delivery defect rather than being clamped to zero. Timing eligibility states whether a customer restriction excluded the occurrence from the internal target cohort. An identifier outside the verified principal's organization, project or environment is indistinguishable from an absent occurrence.