ci: tighten crowdin and i18n PR checks

.github/workflows/precheck.yml

@@ -2,6 +2,10 @@
 name: PR Precheck
 on: [pull_request]
 
+permissions:
+  contents: read
+  issues: write
+
 jobs:
   conflict-check:
     runs-on: ubuntu-24.04
@@ -11,19 +15,37 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.sha }}
       - name: Check Conflicts
         id: check-conflicts
+        env:
+          BASE_REF: ${{ github.event.pull_request.base.ref }}
         run: |
-          git fetch origin main
-          $conflicts = git diff --name-only --diff-filter=U origin/main...HEAD
-          if ($conflicts) {
-            echo "conflict=true" >> $env:GITHUB_OUTPUT
-            Write-Host "Conflicts detected in files: $conflicts"
-          } else {
-            echo "conflict=false" >> $env:GITHUB_OUTPUT
-            Write-Host "No conflicts detected"
-          }
-        shell: pwsh
+          set -euo pipefail
+
+          git fetch origin "$BASE_REF":"refs/remotes/origin/$BASE_REF" --depth=1
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git config user.name "github-actions[bot]"
+
+          if git merge --no-commit --no-ff "origin/$BASE_REF" > /tmp/precheck-merge.log 2>&1; then
+            echo "conflict=false" >> "$GITHUB_OUTPUT"
+            echo "No conflicts detected against origin/$BASE_REF"
+            git merge --abort > /dev/null 2>&1 || true
+            exit 0
+          fi
+
+          if git diff --name-only --diff-filter=U | grep -q .; then
+            echo "conflict=true" >> "$GITHUB_OUTPUT"
+            echo "Conflicts detected against origin/$BASE_REF:"
+            git diff --name-only --diff-filter=U
+          else
+            echo "conflict=false" >> "$GITHUB_OUTPUT"
+            echo "Merge check returned non-zero without unmerged files against origin/$BASE_REF"
+            cat /tmp/precheck-merge.log
+          fi
+
+          git merge --abort > /dev/null 2>&1 || true
+        shell: bash
   labeler:
     runs-on: ubuntu-24.04
     needs: conflict-check