ci(openkal-cross): say what the Windows host provides for the mingw target

The Windows job of this workflow was green with one sandbox lineage and
red with the next on the same sources and the same runner image (PR #629:
lld could not find -lntdll and its neighbours). On a Windows host
openkal-windows's build program generates no import libraries, so where
lld finds them is a property of the host, the sandbox or the payload, and
nothing in the job said which. This step prints it.

Author: speak-agent

.github/workflows/openkal-cross.yml

@@ -187,6 +187,27 @@ jobs:
           "$MCPP_UNDER_TEST" toolchain install llvm 22.1.8
           "$MCPP_UNDER_TEST" toolchain default 'llvm@22.1.8'
 
+      # WHAT THIS RUNNER ACTUALLY PROVIDES FOR THE mingw TARGET. On a Windows
+      # host `openkal-windows`'s build program generates no import libraries
+      # ("the system's own are present"), so `-lntdll` and its neighbours are
+      # found by lld only where the host, the sandbox or the payload puts
+      # them. This job was green with one sandbox lineage and red with the
+      # next (2026-09-13, PR #629, same sources, same image), which is the
+      # signature of a dependency on cached state nobody declared. The lines
+      # below say where the libraries come from, so the next such reading is
+      # diagnosed from the log rather than from a bisect over caches.
+      - name: What this host provides for x86_64-w64-windows-gnu
+        if: matrix.host == 'windows'
+        run: |
+          echo "PATH=$PATH" | tr ':' '\n' | head -40
+          ls "${MCPP_HOME:-$HOME/.mcpp}/registry/data/xpkgs" 2>/dev/null || echo "(no xpkgs dir)"
+          CLANG=$(ls "${MCPP_HOME:-$HOME/.mcpp}"/registry/data/xpkgs/xim-x-llvm/22.1.8/bin/clang++.exe 2>/dev/null | head -1)
+          echo "clang=$CLANG"
+          [ -n "$CLANG" ] && "$CLANG" --target=x86_64-w64-windows-gnu -print-search-dirs
+          [ -n "$CLANG" ] && "$CLANG" --target=x86_64-w64-windows-gnu -print-file-name=libntdll.a
+          [ -n "$CLANG" ] && "$CLANG" --target=x86_64-w64-windows-gnu -print-file-name=libkernel32.a
+          command -v x86_64-w64-mingw32-gcc gcc 2>/dev/null || true
+
       - name: The program — one source, three targets
         run: |
           set -euo pipefail