fix(ci): cap core shard checkout stalls

.github/workflows/ci.yml

@@ -648,20 +648,51 @@ jobs:
       matrix: ${{ fromJson(needs.preflight.outputs.checks_node_core_test_matrix) }}
     steps:
       - name: Checkout
-        id: checkout
-        uses: actions/checkout@v6
-        timeout-minutes: 2
-        continue-on-error: true
-        with:
-          persist-credentials: false
-          submodules: false
+        shell: bash
+        env:
+          CHECKOUT_REPO: ${{ github.repository }}
+          CHECKOUT_SHA: ${{ github.sha }}
+          CHECKOUT_TOKEN: ${{ github.token }}
+        run: |
+          set -euo pipefail
 
-      - name: Checkout (retry)
-        if: steps.checkout.outcome == 'failure'
-        uses: actions/checkout@v6
-        with:
-          persist-credentials: false
-          submodules: false
+          workdir="$GITHUB_WORKSPACE"
+          auth_header="$(printf 'x-access-token:%s' "$CHECKOUT_TOKEN" | base64 | tr -d '\n')"
+
+          reset_checkout_dir() {
+            mkdir -p "$workdir"
+            find "$workdir" -mindepth 1 -maxdepth 1 -exec rm -rf {} +
+          }
+
+          checkout_attempt() {
+            local attempt="$1"
+
+            reset_checkout_dir
+            git init "$workdir" >/dev/null
+            git config --global --add safe.directory "$workdir"
+            git -C "$workdir" remote add origin "https://github.com/${CHECKOUT_REPO}"
+            git -C "$workdir" config gc.auto 0
+
+            timeout --signal=TERM 30s git -C "$workdir" \
+              -c protocol.version=2 \
+              -c "http.https://github.com/.extraheader=AUTHORIZATION: basic ${auth_header}" \
+              fetch --no-tags --prune --no-recurse-submodules --depth=1 origin \
+              "+${CHECKOUT_SHA}:refs/remotes/origin/ci-target"
+
+            git -C "$workdir" checkout --force --detach "$CHECKOUT_SHA"
+            echo "checkout attempt ${attempt}/2 succeeded"
+          }
+
+          for attempt in 1 2; do
+            if checkout_attempt "$attempt"; then
+              exit 0
+            fi
+            echo "checkout attempt ${attempt}/2 failed"
+            sleep $((attempt * 5))
+          done
+
+          echo "checkout failed after 2 attempts" >&2
+          exit 1
 
       - name: Setup Node environment
         uses: ./.github/actions/setup-node-env