chore: restore PR-based changelog automation with auto-merge

Co-authored-by: Isthimius <11380950+Isthimius@users.noreply.github.com>

Author: Copilot

.github/workflows/changelog-master.yml

@@ -295,18 +295,62 @@ jobs:
           validate_changes
           echo "has_changes=true" >> "$GITHUB_OUTPUT"
 
-      - name: Commit and push changelog updates
+      - name: Open changelog update pull request
         if: steps.changes.outputs.has_changes == 'true'
-        shell: bash
-        run: |
-          git config user.name "github-actions[bot]"
-          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
-          git add -- CHANGELOG.md ':(glob)**/CHANGELOG.md'
-          git commit -m "docs: update unreleased changelogs [skip release notes]"
-          git push origin HEAD:master
+        id: changelog_pr
+        uses: peter-evans/create-pull-request@5f6978faf089d4d20b00c7766989d076bb2fc7f1 # v8.1.1
+        with:
+          token: ${{ github.token }}
+          branch: automation/update-changelogs
+          base: master
+          delete-branch: true
+          commit-message: "docs: update unreleased changelogs [skip release notes]"
+          title: "docs: update unreleased changelogs"
+          body: |
+            Automated changelog refresh for commits merged into `master`.
+          author: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
+          committer: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
+          add-paths: |
+            CHANGELOG.md
+            **/CHANGELOG.md
+
+      - name: Enable auto-merge for changelog pull request
+        if: steps.changes.outputs.has_changes == 'true' && steps.changelog_pr.outputs.pull-request-number != ''
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const owner = context.repo.owner;
+            const repo = context.repo.repo;
+            const pull_number = Number("${{ steps.changelog_pr.outputs.pull-request-number }}");
+            const { data: pull } = await github.rest.pulls.get({
+              owner,
+              repo,
+              pull_number
+            });
+
+            if (pull.state !== "open") {
+              core.info(`Changelog PR #${pull_number} is not open; skipping auto-merge enablement.`);
+              return;
+            }
+
+            if (pull.auto_merge) {
+              core.info(`Auto-merge already enabled for changelog PR #${pull_number}.`);
+              return;
+            }
+
+            await github.graphql(
+              `mutation EnableAutoMerge($pullRequestId: ID!) {
+                enablePullRequestAutoMerge(input: { pullRequestId: $pullRequestId, mergeMethod: SQUASH }) {
+                  pullRequest { number }
+                }
+              }`,
+              { pullRequestId: pull.node_id }
+            );
+
+            core.info(`Enabled auto-merge for changelog PR #${pull_number}.`);
 
       - name: Close stale changelog automation pull requests
-        if: always()
+        if: steps.changes.outputs.has_changes != 'true'
         uses: actions/github-script@v7
         with:
           script: |

Tooling/scripts/README.md

@@ -131,7 +131,7 @@ Packs `Tooling/Gondwana.Templates` and reinstalls the exact freshly packed templ
 
 ### `Generate-Project-Changelogs.ps1`
 
-Generates a `CHANGELOG.md` for each library project using [`git-cliff`](https://git-cliff.org/), filtering commits by changed file paths so each project only shows the changes that affected it. This is the standard monorepo approach described in the git-cliff docs. `release.ps1` invokes this script as part of the release flow, and `.github/workflows/changelog-master.yml` refreshes the running unreleased sections after non-changelog pushes to `master` before auto-committing the resulting changelog updates back to `master`.
+Generates a `CHANGELOG.md` for each library project using [`git-cliff`](https://git-cliff.org/), filtering commits by changed file paths so each project only shows the changes that affected it. This is the standard monorepo approach described in the git-cliff docs. `release.ps1` invokes this script as part of the release flow, and `.github/workflows/changelog-master.yml` refreshes the running unreleased sections after non-changelog pushes to `master` before opening/updating an automation PR that is configured for auto-merge.
 
 **What it does:**
 1. Iterates over the default set of library/tooling projects (all `Gondwana.*` projects and `Tooling/*` projects; Demos and `Gondwana.Tests` are excluded).
@@ -176,7 +176,7 @@ Generates a `CHANGELOG.md` for each library project using [`git-cliff`](https://
 
 ### `Generate-Root-Changelog.ps1`
 
-Regenerates only the repository-level `CHANGELOG.md`'s leading derived section while preserving all existing released history exactly. Its entries are grouped by project/area in the same format used by release notes. `.github/workflows/changelog-master.yml` runs this script alongside `Generate-Project-Changelogs.ps1` after non-changelog pushes to `master` before auto-committing any generated changelog changes.
+Regenerates only the repository-level `CHANGELOG.md`'s leading derived section while preserving all existing released history exactly. Its entries are grouped by project/area in the same format used by release notes. `.github/workflows/changelog-master.yml` runs this script alongside `Generate-Project-Changelogs.ps1` after non-changelog pushes to `master` before opening/updating an automation PR that is configured for auto-merge.
 
 **What it does:**
 1. Loads the project/area definitions from `Changelog-ProjectGroups.ps1`.