main: promote dev with a merge commit, not a squash

.github/RELEASING.md

@@ -42,8 +42,9 @@ it cannot be deleted, so direct pushes are fine too.
 
 `main` moves only by promotion: a pull request `dev → main`, which also builds every platform's
 engines, needs a green `CI`, and only an admin can merge. Every version released is a tag on
-`main`. main only squash-merges, so after every push to main the `sync-dev` job in `release.yml`
-merges main back into dev; a hotfix that conflicts with dev pushes nothing and opens an issue with
+`main`. A promotion is merged with a merge commit, never squashed, so main shares dev's history and
+"dev is N commits ahead" counts only unreleased work. Merge work into dev with squash. After every
+push to main the `sync-dev` job in `release.yml` merges main back into dev; a hotfix that conflicts with dev pushes nothing and opens an issue with
 the commands to resolve it by hand.
 
 ## Nightly

.github/scripts/protect-main.sh

@@ -14,7 +14,8 @@
 #   - the `CI` check must pass, evaluated against an up-to-date branch
 #   - only the repository ADMIN role may merge into main (ruleset main-merge-admins):
 #     anyone can open a pull request, an admin merges it, their own included
-#   - linear history: squash or rebase, no merge bubbles
+#   - a promotion lands as a merge commit, never a squash: main then shares dev's history, so
+#     "dev is N commits ahead" counts only what is not on main yet
 #   - a release tag (v*) can be created but never moved or deleted: npm will not
 #     republish a version, so a tag that moved would name a tree nobody installed
 #
@@ -41,7 +42,6 @@ payload="$(cat <<'JSON'
   "rules": [
     { "type": "deletion" },
     { "type": "non_fast_forward" },
-    { "type": "required_linear_history" },
     {
       "type": "pull_request",
       "parameters": {
@@ -51,7 +51,7 @@ payload="$(cat <<'JSON'
         "require_last_push_approval": false,
         "require_extra_approval_for_unattributed_changes": false,
         "required_review_thread_resolution": true,
-        "allowed_merge_methods": ["squash", "rebase"]
+        "allowed_merge_methods": ["merge"]
       }
     },
     {
@@ -156,12 +156,13 @@ apply_ruleset main-merge-admins "$merge_payload"
 apply_ruleset protect-dev "$dev_payload"
 apply_ruleset protect-release-tags "$tag_payload"
 
-# Merge-method hygiene lives on the repository, not the ruleset: squash-only, and
+# Merge-method hygiene lives on the repository: squash for work into dev, merge commits allowed so that
+# protect-main can require them for a promotion (a repository setting cannot differ per branch), and
 # delete the branch once it has landed so the branch list stops accumulating the
 # stale aliases this repo has collected before.
 gh api -X PATCH "repos/$REPO" \
   -F allow_squash_merge=true \
-  -F allow_merge_commit=false \
+  -F allow_merge_commit=true \
   -F allow_rebase_merge=false \
   -F delete_branch_on_merge=true \
   -F allow_auto_merge=true >/dev/null

.github/workflows/release.yml

@@ -85,10 +85,9 @@ jobs:
           echo "::notice::drafted $tag — review it under Releases and publish it to ship to npm"
 
   # ── keep dev on top of main ─────────────────────────────────────────────────
-  # main only takes squash merges, so a promotion from dev lands on main as a NEW
-  # commit that dev does not have; without this, the next dev→main pull request
-  # shows the old work again. Merging main back into dev records that it is
-  # already there. A promotion merges cleanly (same content both sides); a hotfix
+  # A promotion from dev lands on main as a merge commit that dev does not have
+  # yet, and a hotfix straight to main is a commit dev lacks too; merging main
+  # back into dev records that they are already there. A promotion merges cleanly (same content both sides); a hotfix
   # that went straight to main and touches lines dev has since changed does not,
   # and then nothing is pushed: an issue says how to resolve it by hand.
   sync-dev: