diag: buildkit network probe (temp)

Author: new-usemame

.github/workflows/diag-pbs2.yml

@@ -0,0 +1,23 @@
+name: diag-pbs2
+on:
+  push:
+    branches: [diag/pbs-buildkit]
+permissions:
+  contents: read
+jobs:
+  probe:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: docker/setup-buildx-action@v3
+        with:
+          buildkitd-flags: --allow-insecure-entitlement network.host
+      - name: Write test Dockerfile
+        run: |
+          mkdir -p t
+          printf 'FROM ubuntu:noble\nRUN apt-get update >/dev/null && apt-get install -y curl >/dev/null\nRUN curl -fsSL -r 0-0 "https://github.com/astral-sh/python-build-standalone/releases/download/20260623/cpython-3.13.14+20260623-x86_64-unknown-linux-gnu-install_only.tar.gz" -o /tmp/x && echo PBS-DL-OK\n' > t/Dockerfile
+          cat t/Dockerfile
+      - name: BuildKit default network (expect 404)
+        continue-on-error: true
+        run: docker buildx build --no-cache -f t/Dockerfile t 2>&1 | tail -6
+      - name: BuildKit host network (expect OK)
+        run: docker buildx build --no-cache --network=host --allow network.host -f t/Dockerfile t 2>&1 | tail -6