fix: array_merge P0 + restore check-constants self-test P1 (v0.22.0)

P0: replace `+` array union with array_merge() in
Settings_Fields_Extended::get_fields(). PHP `+` keeps left-side keys
when both arrays are integer-indexed — silently drops all 11 image fields
(indexes 0–10 collide with indexes 0–10 of the local array). array_merge()
is already the operator used by the parent class at class-settings-fields.php:84.

P1: restore `php scripts/check-constants.php --self-test` step in the
check-constants CI job. Step was present in v0.21.0 and accidentally dropped
in the CI rewrite. Script logic is intact; CI now exercises it again.

Also adds SettingsFieldsExtendedTest (3 assertions) as a regression guard:
cardinality (29 = 18 local + 11 image), presence check, and per-field
id/section contract. If a + union ever re-appears, test_get_fields_returns_29_fields
fails with a message naming the root cause.

Agent-Session: engineer-infra-prab-p0fix-20260616

.github/workflows/ci.yml

@@ -46,3 +46,8 @@ jobs:
         # by defined() at the reference site. Prevents the v0.19.0 incident
         # class (constant deleted from bootstrap, test fallback masks the gap).
         run: php scripts/check-constants.php
+      - name: Self-test check-constants scanner
+        # Verifies the scanner itself can detect the failure cases it was
+        # designed to catch. If the scanner regresses, this step fails CI.
+        # Added v0.21.0; restored in v0.22.0 (was accidentally dropped in rewrite).
+        run: php scripts/check-constants.php --self-test

includes/admin/class-settings-fields-extended.php

@@ -35,7 +35,8 @@ class PRAutoBlogger_Settings_Fields_Extended {
 	 * @return array<int, array<string, mixed>>
 	 */
 	public static function get_fields(): array {
-		return array(
+		return array_merge(
+			array(
 			// ── Sources (extended) ──────────────────────────────────────
 			array(
 				'id'          => 'prautoblogger_research_model',
@@ -220,6 +221,7 @@ class PRAutoBlogger_Settings_Fields_Extended {
 				'default'     => '1',
 				'description' => __( 'Add visible borders, padding, and alternating row colors to tables in generated articles.', 'prautoblogger' ),
 			),
-		) + PRAutoBlogger_Settings_Fields_Images::get_fields();
+			), PRAutoBlogger_Settings_Fields_Images::get_fields()
+		);
 	}
 }

tests/unit/Admin/SettingsFieldsExtendedTest.php

@@ -0,0 +1,77 @@
+<?php
+/**
+ * Tests for PRAutoBlogger_Settings_Fields_Extended.
+ *
+ * Pins the cardinality contract on get_fields() so any future split that
+ * accidentally re-introduces a + array union (dropping keys) fails CI
+ * rather than silently at runtime.
+ *
+ * @package PRAutoBlogger\Tests\Admin
+ */
+
+namespace PRAutoBlogger\Tests\Admin;
+
+use PRAutoBlogger\Tests\BaseTestCase;
+
+class SettingsFieldsExtendedTest extends BaseTestCase {
+
+	/**
+	 * Stub WP functions that the settings-field classes invoke.
+	 */
+	protected function setUp(): void {
+		parent::setUp();
+		// Image_Model_Registry checks option cache; return false to use hardcoded list.
+		\Brain\Monkey\Functions\when( 'get_option' )->justReturn( false );
+		\Brain\Monkey\Functions\when( 'update_option' )->justReturn( true );
+		// wp_timezone_string is referenced in schedule-time field description.
+		\Brain\Monkey\Functions\when( 'wp_timezone_string' )->justReturn( 'UTC' );
+	}
+
+	/**
+	 * get_fields() must return exactly 29 fields (18 local + 11 image).
+	 *
+	 * This pins the array_merge fix: if a + operator re-appears the image
+	 * fields are silently dropped to 18 and this test fails CI.
+	 * Count breakdown: 18 schedule/publishing/analytics/display/sources fields
+	 * from the local array + 11 image fields from Settings_Fields_Images.
+	 */
+	public function test_get_fields_returns_29_fields(): void {
+		$fields = \PRAutoBlogger_Settings_Fields_Extended::get_fields();
+		$this->assertCount(
+			29,
+			$fields,
+			'Expected 29 fields (18 local + 11 image). A + union instead of array_merge would return only 18.'
+		);
+	}
+
+	/**
+	 * Every field must carry a non-empty id and a section string.
+	 * This catches a malformed field entry that would fail register_setting().
+	 */
+	public function test_every_field_has_id_and_section(): void {
+		$fields = \PRAutoBlogger_Settings_Fields_Extended::get_fields();
+		foreach ( $fields as $field ) {
+			$this->assertArrayHasKey( 'id', $field, 'Field missing id key' );
+			$this->assertNotEmpty( $field['id'], 'Field has empty id' );
+			$this->assertArrayHasKey( 'section', $field, sprintf( 'Field %s missing section key', $field['id'] ) );
+		}
+	}
+
+	/**
+	 * The image fields from Settings_Fields_Images must all be present.
+	 *
+	 * Checks that prautoblogger_image_enabled (first image field)
+	 * exists in the merged result — if the + union regresses, this field
+	 * would be missing because it is at index 0 in the image array (which
+	 * collides with index 0 in the local array under +).
+	 */
+	public function test_image_fields_present_in_merged_result(): void {
+		$fields = \PRAutoBlogger_Settings_Fields_Extended::get_fields();
+		$ids    = array_column( $fields, 'id' );
+		$this->assertContains(
+			'prautoblogger_image_enabled',
+			$ids,
+			'Enable Image Generation toggle missing — array_merge may have regressed to +'
+		);
+	}
+}