Install native runtime deps for dotnet when missing on bare runners

The self-hosted qa runner's minimal image lacked libstdc++/libgcc, which
dotnet fails on with an obscure symbol-relocation error rather than a
clear "missing dependency" message.

scripts/ci/lib.sh

@@ -52,6 +52,29 @@ ensure_dotnet() {
   fi
   export PATH="$install_dir:$PATH"
   export DOTNET_ROOT="$install_dir"
+
+  ensure_dotnet_native_deps
+}
+
+# The .NET runtime is a native ELF binary that dynamically links libstdc++/libgcc.
+# Bare/minimal images (e.g. the act hostexecutor container) may lack them entirely,
+# which fails as an obscure symbol-relocation error rather than "command not found".
+ensure_dotnet_native_deps() {
+  if ldconfig -p 2>/dev/null | grep -q 'libstdc++\.so\.6'; then
+    return 0
+  fi
+
+  log "libstdc++.so.6 missing; installing native runtime deps for dotnet"
+  if command -v apt-get > /dev/null 2>&1; then
+    local sudo_cmd=""
+    if [[ "$(id -u)" -ne 0 ]] && command -v sudo > /dev/null 2>&1; then
+      sudo_cmd="sudo"
+    fi
+    $sudo_cmd apt-get update -y
+    $sudo_cmd apt-get install -y --no-install-recommends libstdc++6 libgcc-s1 libicu-dev ca-certificates
+  else
+    fail "libstdc++.so.6 missing and apt-get unavailable; install a C++ runtime manually on this runner"
+  fi
 }
 
 # Installs Node.js into $CI_ROOT/.node from the official prebuilt tarball if