AppendEntriesNonContiguousBatch

RaftEngine.batchRefusal bound 2 (#1832): an AppendEntries batch that is not contiguous from its own probe point — some entries[i].index != prevLogIndex + 1 + i.

RaftEngine.logEntryAt computes its offset as index - (snapshotIndex + 1), valid only because indices ascend with no gaps, so a log holding [… 7, MAX-1] resolves the wrong slot or falls out of range for every later lookup. Checkable without trust: the leader states prevLogIndex in the same frame, so the required indices are fully determined by the frame itself.