docs(github-pr-workflow): warn about branch protection loss on private Free repos

src/recipes/software-delivery/skills/github-pr-workflow/skill.md

@@ -133,6 +133,16 @@ When a PR is opened during a session, retrieve the channel ID and thread timesta
 
 If there was no Slack thread (the PR was opened from a Linear ticket alone, or it's a Sam-noticed self-maintenance PR), write `Discussion: none (Sam-noticed during <session_id> on <date>)` so the chain knows there's no thread to ack into and Sam can still attribute the work.
 
+## Branch protection & auto-merge limits (GitHub Free)
+
+Under GitHub's organization Free plan, branch protection rules (including required status checks and required reviews) are **silently and permanently deleted** when a repository's visibility is changed to private (which might occur temporarily to handle security incidents or credential rotations).
+
+The consequence is that `gh pr merge --auto --squash` will see zero branch protection requirements and will **merge the PR instantly** upon creation, bypassing all human review and CI checks.
+
+To guard against unreviewed merges:
+- Before running or relying on `--auto` merge as a review gate on a newly privatized repository, verify if branch protection is actually active (e.g. by running `gh api repos/<owner>/<repo>/branches/main/protection`).
+- If branch protection has been deleted, do NOT use auto-merge; instead, wait for explicit manual review and merge, or coordinate with the operator to restore the branch protection rules.
+
 ## Labels (sam repo only)
 
 When opening a PR on `dembrane/sam`, attach a label per source area the diff touches. This is how reviewers see the tier at a glance without opening the file list.