swift

99cd7c6f - [rbi] Assert distinct singleRegion indices and finish IsolationHistory accessor rename

[rbi] Assert distinct singleRegion indices and finish IsolationHistory accessor rename Two related fixes uncovered while building out the IsolationHistory unit tests: - Partition::singleRegion iterated the raw `indices` argument when populating the element-to-region map, so a repeated element would be inserted (and have a merge note pushed) more than once, which is unrecoverable in popHistory. Rather than silently de-duplicating, trap the caller bug: sort to pick the lowest element as the region representative and assert there are no duplicates. - Finish migrating the IsolationHistory unit tests off the old Node::getParent()/two-arg pushMergeElementRegions API onto getNext() and the (rep, rhs, peers) merge signature introduced in the preceding commits.