chore: import upstream snapshot with attribution

.github/workflows/fuzz.yml

@@ -0,0 +1,109 @@
+name: fuzz
+
+on:
+  push:
+    branches: main
+  pull_request:
+    paths:
+      - .github/workflows/fuzz.yml
+      - scripts/fuzz.py
+  schedule:
+    - cron: "0 0 * * *"
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  fuzz:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        # TODO: add 3.15; relies on libcst which doesn't support 3.15 yet
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+
+    steps:
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
+        with:
+          python-version: ${{ matrix.python-version }}
+          allow-prereleases: true
+          pip-version: "25.3"
+          pip-install: --group tox
+
+      - name: Run fuzz tests
+        id: fuzz
+        run: tox -e fuzz --result-json $python_ver
+        env:
+          python_ver: ${{ matrix.python-version }}
+
+      - uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        if: failure() && steps.fuzz.outcome == 'failure'
+        with:
+          name: ${{ matrix.python-version }}
+          path: ${{ matrix.python-version }}
+
+  create-issue:
+    runs-on: ubuntu-latest
+    needs: fuzz
+    if:
+      github.repository == 'psf/black' && github.event_name != 'pull_request' &&
+      failure()
+    permissions:
+      issues: write # Needed to create issue
+    steps:
+      - uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
+        with:
+          merge-multiple: true
+          path: ./output
+
+      - name: Generate issue data
+        run: |
+          output=issue-body.html
+          touch $output
+          for FILE in ./output/*; do
+            echo "**Python $(basename $FILE)**" >> $output
+            echo -e "\`\`\`py" >> $output
+              echo -e "# stdout:" >> $output
+              echo -e "$(jq .testenvs.fuzz.test[-1].output $FILE -r)\n" >> $output
+              echo -e "# stderr:" >> $output
+              echo -e "$(jq .testenvs.fuzz.test[-1].err $FILE -r)" >> $output
+            echo -e "\`\`\`\n" >> $output
+          done
+
+      - name: Get existing issue
+        id: issue
+        run: |
+          echo "ISSUE=$( gh issue list \
+          -A github-actions[bot] -l 'ci: fuzz error' \
+          --json number -q .[0].number \
+          -R $REPO )" >> $GITHUB_OUTPUT
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+          REPO: ${{ github.repository }}
+
+      - name: Create new issue
+        if: steps.issue.outputs.ISSUE == ''
+        run: >
+          gh issue create -t "Fuzz test failure" -F issue-body.html -l "ci: fuzz error"
+          -R $REPO
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+          REPO: ${{ github.repository }}
+
+      - name: Edit existing issue
+        if: steps.issue.outputs.ISSUE != ''
+        run: gh issue edit $ISSUE -F issue-body.html -R $REPO
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+          REPO: ${{ github.repository }}
+          ISSUE: ${{ steps.issue.outputs.ISSUE }}