UTC-normalized timestamps can lose local-day semantics

A timestamp can preserve an absolute instant while losing the location-local calendar semantics needed for same-day priority. If an upstream producer normalizes a local pickup time to UTC without preserving an authoritative location timezone, do not treat UTC as pickup-local. Preserve a source-local numeric offset when available for bounded classification, fail closed around date-boundary or daylight-saving ambiguity, and prefer an IANA location timezone for the long-term contract.

Applicability and limits: a numeric offset describes one instant, not a timezone rule. It cannot determine future or earlier offsets across transitions, and a UTC instant alone cannot reconstruct the source's intended local calendar date.