What changed — in user terms
The entry names the module, the user names the symptom. 'Split the demo module behind a loader map' is an internal sentence; 'pages without demos got 315 KB lighter' is the same fact in the reader's currency. This site's changelog carries both, and the measured number is the second one.
Who noticed — the provenance line
Entries that came from feedback say so. It costs one clause, it credits the reporter, and it teaches readers that reporting works. 'Fixed' entries are first-class here, not shame-adjacent footnotes.
How to roll back — the exit
A change worth recording is a change someone may need to undo. The rollback note can be a sentence ('revert the loader map; budgets were re-cut either side'), but it must exist. A changelog without exits is a marketing feed.