Internal
A committed index raft withheld from the application: the internal §5.4.2 election no-op (LogEntry.isNoOp) or a §6 membership-change entry (LogEntry.config).
Carries index and nothing else — deliberately. The entry's contents stay withheld because a consumer must never apply raft's own bookkeeping as if it were application data; what the marker restores is only the consumer's ability to say "index index is behind me".
A state machine folds this by advancing its applied index and doing nothing else:
is Committed.Internal -> appliedIndex = committed.indexContent copied to clipboard