fix: Add sequential testing workaround for parallel test issue

Workaround for Issue #62: Parallel test execution causes intermittent
TenantKey unwrap failures (~1-10% failure rate).

This temporary solution:
- Checks for .preflight-sequential-tests marker file
- Uses sequential testing if marker exists
- Allows PR #61 to proceed while proper fix developed

See: #62

Will be removed when Issue #62 is properly fixed with per-process
KEK files or test isolation improvements.

Author: kevalyq

.preflight-sequential-tests

@@ -0,0 +1,5 @@
+WORKAROUND for Issue #62: Parallel test execution causes intermittent failures
+See: https://github.com/SecPal/api/issues/62
+
+This file forces sequential test execution in preflight.sh until the issue is resolved.
+Remove this file once parallel test isolation is fixed.

.preflight-sequential-tests.license

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: 2025 SecPal Contributors
+
+SPDX-License-Identifier: AGPL-3.0-or-later

scripts/preflight.sh

@@ -68,11 +68,20 @@ run_phpstan() {
 run_tests() {
   local cmd_prefix="$1"
   local test_exit=0
+
+  # WORKAROUND: Parallel test execution has intermittent failures (Issue #62)
+  # Use sequential testing until fixed
+  # See: https://github.com/SecPal/api/issues/62
+  local parallel_flag=""
+  if [ ! -f .preflight-sequential-tests ]; then
+    parallel_flag="--parallel"
+  fi
+
   # Run tests (Laravel Artisan → Pest → PHPUnit)
   if [ -f artisan ]; then
-    ${cmd_prefix} php artisan test --parallel || test_exit=$?
+    ${cmd_prefix} php artisan test ${parallel_flag} || test_exit=$?
   elif [ -x ./vendor/bin/pest ]; then
-    ${cmd_prefix} ./vendor/bin/pest --parallel || test_exit=$?
+    ${cmd_prefix} ./vendor/bin/pest ${parallel_flag} || test_exit=$?
   elif [ -x ./vendor/bin/phpunit ]; then
     ${cmd_prefix} ./vendor/bin/phpunit || test_exit=$?
   fi