Absorb `incoming` (dedup by `Rev`) and canonically re-sort the whole combined history. The sort is deterministic (topological, ties broken by `Rev`), so two peers that absorb the same delta set produce byte-identical history, not merely two different valid orderings. This is the history-convergence mechanism: arrival order is erased. Callers update the registry separately (LWW apply is commutativ
(&mut self, incoming: impl IntoIterator<Item = Delta>)
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