fix(installer): fail closed on test enumeration errors

tools/install-state-machine.test.sh

@@ -8,6 +8,8 @@
 set -uo pipefail
 
 ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+# shellcheck source=tools/test-enumeration-assertions.sh
+source "$ROOT/tools/test-enumeration-assertions.sh"
 TMP="$(mktemp -d "${TMPDIR:-/tmp}/mosaic-install-state-test.XXXXXX")"
 trap 'rm -rf "$TMP"' EXIT
 failures=0
@@ -396,7 +398,8 @@ set -e
 grep -q '^\[P0\] FAIL:.*unsafe context' "$TMP/symlink-target.log" \
   && pass_case 'symlinked rollback parent was rejected by P0' \
   || fail_case 'symlinked rollback parent lacked an attributable P0 failure'
-[[ -z "$(find "$symlink_outside" -mindepth 1 -print -quit)" ]] || fail_case 'symlink target was mutated'
+test_assert_find_empty 'symlink target mutation check' "$symlink_outside" -mindepth 1 \
+  || fail_case 'symlink target was mutated or could not be enumerated'
 
 printf '[test] case: journal initialization failure is fatal before mutation\n'
 journal_home="$TMP/journal-failure/home"