Reject unreadable UCE source units

scripts/test_dependency_invalidation.sh

@@ -54,6 +54,23 @@ if [[ "$(http_marker)" != *"dependency-marker-a"* ]]; then
 	exit 1
 fi
 
+printf '%s\n' 'CLI(Request& context) { print("readable-source-marker"); }' >"$source_dir/unreadable.uce"
+chmod 000 "$source_dir/unreadable.uce"
+if unreadable_output=$(scripts/uce-cli "/$test_name/unreadable.uce" 2>&1); then
+	echo "unreadable source unexpectedly compiled: $unreadable_output" >&2
+	exit 1
+fi
+if [[ "$unreadable_output" != *"source file is not readable"* ]]; then
+	echo "unreadable source did not report its actual compile error: $unreadable_output" >&2
+	exit 1
+fi
+if [[ -e "$cache_dir/unreadable.uce.wasm" ]]; then
+	echo "unreadable source published a wasm artifact" >&2
+	exit 1
+fi
+chmod 644 "$source_dir/unreadable.uce"
+assert_marker unreadable readable-source-marker
+
 sed -i 's/dependency-marker-a/dependency-marker-b/' "$source_dir/child.uce"
 started_at=$(date +%s%N)
 http_during_rebuild=$(http_marker)