git notes
Annotations hung on published commits, rewriting nothing.
A commit message is immutable once published — but notes hangs a plaque beside it: free text, kept under refs/notes/, displayed by log next to the commit and editable without touching any hash.
It is for what you learn late: the benchmark result, the link to the incident the commit caused, the review number. Notes don't travel with push by default — sharing them means pushing refs/notes/* on purpose.
$ git notes add -m "medido: build 18% mais rápido" 7ad3fd3
$ git notes show 7ad3fd3
medido: build 18% mais rápido