[CI] Add OBS cache for pre-commit hooks (vllm-project#12857)

## What this PR does / why we need it?

Add OBS-based caching for pre-commit hooks to speed up PR CI.

### Changes:

1. **Add push_build_precommit_cache.yaml** (new file):
- Triggers on push to main when .pre-commit-config.yaml or
equirements-lint.txt changes
- Runs pre-commit to populate the cache, then uploads to OBS
(^Gscend-ci-cache-hk bucket)
- Uses sha256sum for cache key (not hashFiles() which returns empty on
self-hosted runners)
- Uses /tmp/pre-commit-cache (ephemeral) instead of ~/.cache/pre-commit
(PVC) to ensure cache comes from OBS, not local disk residue
- Requires secrets HW_OBS_AK_HK and HW_OBS_SK_HK to be configured in
repository settings

2. **Modify pr_test.yaml**:
- Add uns-on/cache/restore@v5 step before "Run pre-commit" to restore
cache from OBS
- Fork PRs can read the cache using the runner's built-in read-only
AK/SK (no secrets needed)
   - Same PRE_COMMIT_HOME: /tmp/pre-commit-cache path

### Principle:
- **Write cache**: only on main branch (push trigger), using GitHub
secrets for write credentials
- **Read cache**: all PRs (including fork PRs), using runner's built-in
read-only AK/SK

### Prerequisites:
- Configure HW_OBS_AK_HK and HW_OBS_SK_HK secrets in repository settings
(Actions → Secrets)
- Ensure runners have obs-cache-credentials secret in their pod template
for read-only access

## Does this PR introduce any user-facing change?

No.

## How was this patch tested?

Verified on ^Gscend-gha-runners/vllm-ascend fork — cache write and read
both confirmed working.

- vLLM version: v0.25.1
- vLLM main:
vllm-project/vllm@fe784ff

---------

Signed-off-by: ZhangYang <1079854335@qq.com>

Author: KadenZhang3321

.github/workflows/pr_test.yaml

@@ -145,7 +145,25 @@ jobs:
           git config --global --add safe.directory "$GITHUB_WORKSPACE"
           chmod +x .github/workflows/scripts/gitleaks.sh
           .github/workflows/scripts/gitleaks.sh
-          
+
+      - name: Get pre-commit config hash
+        id: get_hash
+        run: |
+          PRE_COMMIT_HASH=$(sha256sum .pre-commit-config.yaml | awk '{print $1}')
+          echo "PRE_COMMIT_HASH=$PRE_COMMIT_HASH" >> $GITHUB_OUTPUT
+
+      - name: Restore pre-commit cache
+        uses: runs-on/cache/restore@v5
+        env:
+          RUNS_ON_S3_BUCKET_CACHE: ascend-ci-cache-hk
+          RUNS_ON_S3_BUCKET_ENDPOINT: https://obs.ap-southeast-1.myhuaweicloud.com
+          RUNS_ON_S3_FORCE_PATH_STYLE: "false"
+          AWS_S3_FORCE_PATH_STYLE: "false"
+          AWS_REGION: ap-southeast-1
+        with:
+          path: /tmp/pre-commit-cache
+          key: pre-commit-${{ steps.get_hash.outputs.PRE_COMMIT_HASH }}
+
       - name: Run pre-commit
         env:
           PRE_COMMIT_HOME: /tmp/pre-commit-cache

.github/workflows/push_build_precommit_cache.yaml

@@ -0,0 +1,95 @@
+#
+# Copyright (c) 2026 Huawei Technologies Co., Ltd. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# This file is a part of the vllm-ascend project.
+#
+
+# This workflow populates the pre-commit cache in OBS on push to main.
+# Fork PRs can then restore this cache read-only using the runner's built-in AK/SK.
+name: 'Cache pre-commit'
+on:
+  push:
+    branches: ["main"]
+    paths:
+      - '.pre-commit-config.yaml'
+      - 'requirements-lint.txt'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+defaults:
+  run:
+    shell: bash -el {0}
+
+concurrency:
+  group: precommit-cache-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build-cache:
+    runs-on: linux-amd64-cpu-8-hk
+    container:
+      image: quay.io/ascend-ci/vllm-ascend:lint
+    env:
+      RUNS_ON_S3_BUCKET_CACHE: ascend-ci-cache-hk
+      RUNS_ON_S3_BUCKET_ENDPOINT: https://obs.ap-southeast-1.myhuaweicloud.com
+      RUNS_ON_S3_FORCE_PATH_STYLE: "false"
+      AWS_S3_FORCE_PATH_STYLE: "false"
+      AWS_REGION: ap-southeast-1
+      RUNS_ON_RUNNER_NAME: ""
+      AWS_ACCESS_KEY_ID: ${{ secrets.HW_OBS_AK }}
+      AWS_SECRET_ACCESS_KEY: ${{ secrets.HW_OBS_SK }}
+    steps:
+      - name: Checkout vllm-project/vllm-ascend repo
+        uses: actions/checkout@v7
+        with:
+          fetch-depth: 0
+
+      - name: Get pre-commit config hash
+        id: get_hash
+        run: |
+          PRE_COMMIT_HASH=$(sha256sum .pre-commit-config.yaml | awk '{print $1}')
+          echo "PRE_COMMIT_HASH=$PRE_COMMIT_HASH" >> $GITHUB_OUTPUT
+
+      - name: Check if cache exists
+        id: check-cache
+        uses: runs-on/cache/restore@v5
+        with:
+          path: /tmp/pre-commit-cache
+          key: pre-commit-${{ steps.get_hash.outputs.PRE_COMMIT_HASH }}
+          lookup-only: true
+
+      - name: Clean stale pre-commit cache
+        if: steps.check-cache.outputs.cache-hit != 'true'
+        run: rm -rf /tmp/pre-commit-cache
+
+      - name: Run pre-commit (populate cache)
+        if: steps.check-cache.outputs.cache-hit != 'true'
+        env:
+          PRE_COMMIT_HOME: /tmp/pre-commit-cache
+          PRE_COMMIT_COLOR: always
+          FORCE_COLOR: "1"
+          TERM: xterm-256color
+          SHELLCHECK_OPTS: "--exclude=SC2046,SC2006,SC2086"
+        run: |
+          git config --global --add safe.directory /__w/vllm-ascend/vllm-ascend
+          pre-commit run --all-files --hook-stage manual --show-diff-on-failure
+
+      - name: Save pre-commit cache
+        if: always() && steps.check-cache.outputs.cache-hit != 'true'
+        uses: runs-on/cache/save@v5
+        with:
+          path: /tmp/pre-commit-cache
+          key: pre-commit-${{ steps.get_hash.outputs.PRE_COMMIT_HASH }}