feat(linux): gate graphical backends and capabilities

.github/workflows/headless-portability.yml

@@ -63,6 +63,16 @@ jobs:
         with:
           dotnet-version: "10.0.x"
 
+      - name: Install Linux graphical smoke dependencies
+        shell: bash
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends \
+            libgl1-mesa-dri \
+            mesa-utils \
+            xauth \
+            xvfb
+
       - name: Build presentation-free closure
         shell: pwsh
         run: |
@@ -140,7 +150,7 @@ jobs:
           dotnet test `
             tests/AcDream.App.Tests/AcDream.App.Tests.csproj `
             -c Release `
-            --filter "FullyQualifiedName~LinuxMonotonicFramePacingWaiterTests|FullyQualifiedName~LinuxPlatformBoundaryTests|FullyQualifiedName~GraphicalHostPlatformServicesTests|FullyQualifiedName~GraphicalLegacyConfigurationMigratorTests"
+            --filter "FullyQualifiedName~LinuxMonotonicFramePacingWaiterTests|FullyQualifiedName~LinuxPlatformBoundaryTests|FullyQualifiedName~GraphicalHostPlatformServicesTests|FullyQualifiedName~GraphicalLegacyConfigurationMigratorTests|FullyQualifiedName~GraphicalWindowBackendSelectionTests|FullyQualifiedName~GraphicalCapabilityRequirementsTests|FullyQualifiedName~StudioWindowTests"
           if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
 
       - name: Verify Linux package contract
@@ -169,3 +179,26 @@ jobs:
             src/AcDream.App \
             --exclude='FramePacingWaiterFactory.cs' \
             --exclude='WindowsHighResolutionFramePacingWaiter.cs'
+
+      - name: Verify actionable unsupported-driver gate
+        shell: bash
+        run: |
+          set -euo pipefail
+          root=artifacts/acdream-linux-x64
+          report=artifacts/linux-x11-capabilities.json
+          set +e
+          ACDREAM_DISPLAY_PROTOCOL=x11 \
+            xvfb-run -a "$root/AcDream.App" \
+              ui-studio /tmp/not-needed \
+              --mockup \
+              --capability-report "$report"
+          code=$?
+          set -e
+
+          test "$code" -eq 4
+          test "$(jq -r '.ActiveDisplayProtocol' "$report")" = X11
+          test "$(jq -r '.Lifecycle.ShutdownComplete' "$report")" = true
+          test "$(jq -r '.Lifecycle.OwnedWindowCount' "$report")" -eq 0
+          test "$(jq -r '.Lifecycle.OwnedGlApiCount' "$report")" -eq 0
+          test "$(jq -r '.Lifecycle.OwnedInputContextCount' "$report")" -eq 0
+          jq -e '.SupportFailures | length > 0' "$report"