Add Linux core validation workflow

.github/workflows/core-validation.yml

@@ -0,0 +1,59 @@
+name: Core validation
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: core-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  core:
+    name: Linux core gate
+    runs-on: ubuntu-24.04
+    timeout-minutes: 15
+    env:
+      DOTNET_CLI_TELEMETRY_OPTOUT: "1"
+      DOTNET_NOLOGO: "true"
+      NUGET_XMLDOC_MODE: skip
+      PYTHONUTF8: "1"
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+
+      - name: Set up Python 3.11
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+        with:
+          python-version: "3.11"
+          architecture: x64
+
+      - name: Set up .NET SDK
+        uses: actions/setup-dotnet@c2fa09f4bde5ebb9d1777cf28262a3eb3db3ced7 # v5.2.0
+        with:
+          global-json-file: global.json
+
+      - name: Report toolchain
+        run: |
+          python --version
+          dotnet --version
+
+      - name: Run asset-independent validation
+        run: python -X utf8 tools/validate.py --level core
+
+      - name: Upload failure logs
+        if: failure()
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: core-validation-${{ github.run_id }}-${{ github.run_attempt }}
+          path: build/validation/**
+          if-no-files-found: ignore
+          retention-days: 7