fix(backtrack): lock all target branches upfront, unlock one-at-a-time for each merge

Agent-Logs-Url: https://github.com/petesramek/polyline-algorithm-csharp/sessions/5ea2e5f9-89e1-4d12-8aeb-bc33b2df85b3

Co-authored-by: petesramek <2333452+petesramek@users.noreply.github.com>

Author: Copilot

.github/workflows/backtrack.yml

@@ -69,6 +69,32 @@ jobs:
           token: ${{ secrets.GH_ADMIN_TOKEN }}
           lock-branch: 'true'
 
+      - name: 'Lock preview branch'
+        id: lock-preview
+        if: ${{ steps.targets.outputs.preview-branch != '' }}
+        uses: './.github/actions/github/branch-protection/lock'
+        with:
+          branch: ${{ steps.targets.outputs.preview-branch }}
+          token: ${{ secrets.GH_ADMIN_TOKEN }}
+          lock-branch: 'true'
+
+      - name: 'Lock develop branch'
+        id: lock-develop
+        if: ${{ steps.check-develop.outputs.exists == 'true' }}
+        uses: './.github/actions/github/branch-protection/lock'
+        with:
+          branch: ${{ steps.targets.outputs.develop-branch }}
+          token: ${{ secrets.GH_ADMIN_TOKEN }}
+          lock-branch: 'true'
+
+      - name: 'Unlock preview branch for merge'
+        if: ${{ steps.targets.outputs.preview-branch != '' }}
+        uses: './.github/actions/github/branch-protection/lock'
+        with:
+          branch: ${{ steps.targets.outputs.preview-branch }}
+          token: ${{ secrets.GH_ADMIN_TOKEN }}
+          lock-branch: 'false'
+
       - name: 'Backtrack: merge ${{ github.base_ref }} into ${{ steps.targets.outputs.preview-branch }}'
         if: ${{ steps.targets.outputs.preview-branch != '' }}
         env:
@@ -79,6 +105,14 @@ jobs:
             --field head="${{ github.base_ref }}" \
             --field commit_message="Backtrack: merge ${{ github.base_ref }} into ${{ steps.targets.outputs.preview-branch }}"
 
+      - name: 'Unlock develop branch for merge'
+        if: ${{ steps.check-develop.outputs.exists == 'true' }}
+        uses: './.github/actions/github/branch-protection/lock'
+        with:
+          branch: ${{ steps.targets.outputs.develop-branch }}
+          token: ${{ secrets.GH_ADMIN_TOKEN }}
+          lock-branch: 'false'
+
       - name: 'Backtrack: merge ${{ steps.targets.outputs.merge-source }} into ${{ steps.targets.outputs.develop-branch }}'
         if: ${{ steps.check-develop.outputs.exists == 'true' }}
         env:
@@ -97,6 +131,22 @@ jobs:
           token: ${{ secrets.GH_ADMIN_TOKEN }}
           lock-branch: 'false'
 
+      - name: 'Restore protection: preview branch'
+        if: ${{ always() && steps.lock-preview.outcome == 'success' }}
+        uses: './.github/actions/github/branch-protection/lock'
+        with:
+          branch: ${{ steps.targets.outputs.preview-branch }}
+          token: ${{ secrets.GH_ADMIN_TOKEN }}
+          lock-branch: 'false'
+
+      - name: 'Restore protection: develop branch'
+        if: ${{ always() && steps.lock-develop.outcome == 'success' }}
+        uses: './.github/actions/github/branch-protection/lock'
+        with:
+          branch: ${{ steps.targets.outputs.develop-branch }}
+          token: ${{ secrets.GH_ADMIN_TOKEN }}
+          lock-branch: 'false'
+
       - name: 'Write backtrack summary'
         if: ${{ always() }}
         run: |