diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 85ce30676..2e091a769 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -129,6 +129,7 @@ Contributor requirements (summary):
 - **Link with a closing keyword** — use `Closes #123`, `Fixes #123`, or `Resolves #123` in the PR body. The CI check will fail and the PR will be auto-closed if no valid issue reference is found.
 - **One concern per PR** — bug fixes, enhancements, and features must be separate PRs
 - **No drive-by formatting** — don't reformat code unrelated to your change
+- **Don't bundle test-fixture updates into `docs:` or unrelated commits** — when a production change makes an existing test assertion stale, the test correction MUST land as its own `test:` (or `fix:`) commit, not bundled into a `docs:` commit that also updates the explanation. The release-sdk hotfix cherry-pick filter routes by commit-subject prefix (`fix:`, `chore:`, `test:`); a test-fixture correction packed under a `docs:` prefix is invisible to the picker and ships a half-state to the hotfix branch — production code changed, test assertion stale. v1.42.3 hit this exact mode (#3621). The fix is upstream: keep the test-fixture commit separate.
 - **CI must pass** — all configured matrix jobs must be green. Node 22 remains the compatibility floor; Node 24 is the primary target; Node 26 compatibility must be preserved for code and tests even when a Node 26 CI lane is not yet available.
 - **Scope matches the approved issue** — if your PR does more than what the issue describes, the extra changes will be asked to be removed or moved to a new issue