fix: support piped installer execution

tests/release-scripts.test.sh

@@ -498,6 +498,14 @@ test_release_workflow_uses_scoped_job_token() (
   ! grep -Fq 'vars.GITEA_BASE_URL' "$workflow"
 )
 
+test_installer_runs_when_piped_to_bash() (
+  local output status=0
+  output="$(ERP_GITEA_BASE_URL= bash -s -- --no-service < "$PROJECT_ROOT/install.sh" 2>&1)" || status=$?
+  [[ "$status" -ne 0 ]]
+  [[ "$output" == *'[ERP Install] ERROR:'* ]]
+  [[ "$output" != *'BASH_SOURCE'* ]]
+)
+
 run_test 'erp-run preserves Java option arguments' test_erp_run_preserves_java_option_arguments
 run_test 'installer accepts a correctly signed archive' test_installer_verifies_signed_safe_archive
 run_test 'installer rejects symlinks in release archives' test_installer_rejects_archive_symlinks
@@ -510,6 +518,7 @@ run_test 'noninteractive install reports a missing database password' test_nonin
 run_test 'installer requires an explicit Gitea URL' test_installer_requires_explicit_gitea_url
 run_test 'no-service install disables online update' test_no_service_install_disables_online_update
 run_test 'release workflow uses the scoped Gitea job token' test_release_workflow_uses_scoped_job_token
+run_test 'installer starts correctly when piped to bash' test_installer_runs_when_piped_to_bash
 
 printf 'RESULT pass=%s fail=%s\n' "$PASS" "$FAIL"
 [[ "$FAIL" -eq 0 ]]