Function is_transaction_commit 

pub fn is_transaction_commit(record: &OpRecord) -> bool

True when record is the atomic transaction commit marker.

A TransactionCommit marker carries no user-facing operation: it is the atomic commit sentinel, not a forward op. Undo/redo eligibility scans ignore it so a record-less transaction is never itself selected as an undoable or redoable unit. A batch with at least one non-marker entry still qualifies on that entry.