docs: require committing as you go, in coherent single-concern commits

AGENTS.md

@@ -21,6 +21,25 @@ release notes. Write it for that reader:
 `feat` has to be a word, so `Fix the feature flag leak` is a patch. Only the
 subject line is read; the body is not.
 
+## Commit as you go
+
+Commit each coherent change as you finish it, not once at the end of a session:
+
+- **A commit is the unit the release is built from.** The subject becomes a line
+  in the release notes and the version bump for that push, so a session's work
+  squashed into one commit is one note that describes none of it well.
+- **One change, one concern.** A fix and a feature are two commits even when they
+  touch the same file, because they are two different lines in the notes and two
+  different reasons for a reader to care.
+- **Run `npm test` before each commit**, so no commit in the history is a state
+  the suite would have refused.
+- **Do not batch unrelated work to save commits.** The cost of committing as you
+  go is a little more care; the cost of not doing it is a release log nobody can
+  read and a push that cannot be bisected.
+
+Work still in progress is committed too — the repository is the record, and a
+half-finished change kept in the working tree is a change with no history.
+
 ## The release job owns the version and the changelog
 
 `package.json`'s `version` and `CHANGELOG.md` are the job's to write, derived