Add a test reproducing #13 (#14)

Hopefully a useful first step in making a fix

.github/workflows/ci.yml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4f169fe..79dbb5f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -27,3 +27,9 @@
         ]
       # this ruleset only supports linux and macos
       exclude_windows: true
+  integration-tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - working-directory: examples/target-determinator
+        run: ./minimal_download_test.sh

examples/target-determinator/minimal_download_test.sh

diff --git a/examples/target-determinator/minimal_download_test.sh b/examples/target-determinator/minimal_download_test.sh
new file mode 100755
index 0000000..4ee0b88
--- /dev/null
+++ b/examples/target-determinator/minimal_download_test.sh
@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+
+set -o errexit -o pipefail -o nounset
+
+# Determine a single file we are supposed to download for the host platform
+OS="$(uname | tr '[:upper:]' '[:lower:]')"
+ARCH="$(arch)"
+ALLOWED="target-determinator.${OS}.${ARCH}"
+if [ "$ARCH" == "x86_64" ]; then
+    ALLOWED="target-determinator.${OS}.amd64"
+fi
+
+#############
+# Test bzlmod
+OUTPUT_BASE=$(mktemp -d)
+REPO_CACHE=$(mktemp -d)
+DL_CONFIG=$(mktemp)
+
+# Construct a Bazel downloader config that forbids access to non-allowed files from multitool.lock.json
+for file in target-determinator.darwin.arm64 target-determinator.linux.amd64 target-determinator.darwin.amd64; do
+  if [ "$file" != "$ALLOWED" ]; then
+    cat >$DL_CONFIG <<EOF
+rewrite github.com/bazel-contrib/target-determinator/releases/download/([^/]+)/$file disallowed.build/\$1/$file
+EOF
+  fi
+done
+
+# This build will fail if we attempt a disallowed download
+bazel "--output_base=$OUTPUT_BASE" build \
+  --enable_bzlmod \
+  "--repository_cache=$REPO_CACHE" \
+  "--experimental_downloader_config=$DL_CONFIG" \
+  //:integration_test
+
+#############
+# TODO: Test WORKSPACE