fix(launcher): require executable Linux hosts

.github/workflows/headless-portability.yml

@@ -135,6 +135,13 @@ jobs:
           dotnet run --project src/AcDream.Headless/AcDream.Headless.csproj -c Release -- validate --config headless-k0.json
           if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
 
+      - name: Verify Linux headless host executable permission
+        if: runner.os == 'Linux'
+        shell: bash
+        run: |
+          set -euo pipefail
+          test -x src/AcDream.Headless/bin/Release/net10.0/acdream-headless
+
   portable-launcher:
     strategy:
       fail-fast: false