Sync is a data-model decision, not a network feature
Offline-first only holds if the merge rules are agreed before the first tablet ships. INDO-PIX is offline-first with conflict-safe sync, so a record written on a ward with no signal is reconcilable rather than merely stored, and resolution follows the rule the study agreed rather than the order in which tablets reconnected. Those rules are settled with the clinical lead during technical alignment and written into the architecture record, because a study cannot revise its provenance model after collection has started.