feat(2meet-data-optimizer): guard orphaned flat-table groups

- On init:1, re-register aeav_only groups whose flat table exists and whose definition is in wpdo_registry_meta but no active plugin registers them, so their data stays readable (routing only, never DDL)
- Keys owned by a live group, or with rows in native meta (newer data written while orphaned), are left alone; the native-meta check is cached for a day
- Surface restored groups via Site Health (wpdo_orphaned_entity_groups), the admin Doctor tab, and wp wpdo doctor
- Verify: EntityRegistryRestoreTest (9), OrphanGroupRestoreTest (7); core unit 622 / integration 439, HP 141/49, WC 10/22 OK; dry-run on dev20–22 restores 16/17/4 groups, keeps hp_taxonomy hp_sort_order/hp_icon on native
- PR: PR-018

includes/diagnostic/class-tmdo-site-health.php

@@ -2,7 +2,7 @@
 /**
  * TMDO_Site_Health — WordPress Site Health integration (v2.2.0 M3).
  *
- * Registers 8 tests under Tools → Site Health → Status:
+ * Registers 9 tests under Tools → Site Health → Status:
  *   1. wpdo_schema_drift          (critical)
  *   2. wpdo_error_budget          (recommended)
  *   3. wpdo_hook_conflicts        (recommended)
@@ -11,6 +11,7 @@
  *   6. wpdo_orphan_zone_rows      (recommended)
  *   7. wpdo_missing_snapshot      (critical)
  *   8. wpdo_entity_group_collisions (recommended)
+ *   9. wpdo_orphaned_entity_groups  (recommended)
  *
  * Each test result is cached for 5 minutes to keep Site Health responsive.
  *
@@ -43,6 +44,7 @@ class TMDO_Site_Health {
 		'wpdo_orphan_zone_rows'        => 'check_orphan_zone_rows',
 		'wpdo_missing_snapshot'        => 'check_missing_snapshot',
 		'wpdo_entity_group_collisions' => 'check_entity_group_collisions',
+		'wpdo_orphaned_entity_groups'  => 'check_orphaned_entity_groups',
 	);
 
 	/**
@@ -55,7 +57,7 @@ class TMDO_Site_Health {
 	}
 
 	/**
-	 * Register the 8 tests with WP Site Health.
+	 * Register the 9 tests with WP Site Health.
 	 *
 	 * @param array $tests Existing tests.
 	 * @return array
@@ -86,6 +88,7 @@ class TMDO_Site_Health {
 			'wpdo_orphan_zone_rows'        => __( 'WPDO orphan zone rows', '2meet-data-optimizer' ),
 			'wpdo_missing_snapshot'        => __( 'WPDO missing snapshot', '2meet-data-optimizer' ),
 			'wpdo_entity_group_collisions' => __( 'WPDO entity group collisions', '2meet-data-optimizer' ),
+			'wpdo_orphaned_entity_groups'  => __( 'WPDO orphaned entity groups', '2meet-data-optimizer' ),
 		);
 		return $map[ $key ] ?? $key;
 	}
@@ -468,6 +471,46 @@ class TMDO_Site_Health {
 		);
 	}
 
+	// ─── Test 9: Orphaned entity groups ─────────────────────────────────
+
+	/**
+	 * Report flat-table groups kept alive from wpdo_registry_meta because no
+	 * active plugin registers them any more.
+	 *
+	 * Not cached for the same reason as check_entity_group_collisions().
+	 *
+	 * @return array Site Health result.
+	 */
+	public static function check_orphaned_entity_groups(): array {
+		$restored = class_exists( 'TMDO_Entity_Registry' ) ? TMDO_Entity_Registry::get_restored_groups() : array();
+		if ( empty( $restored ) ) {
+			return self::wrap( 'wpdo_orphaned_entity_groups', self::pass( __( 'Every flat-table group is registered by an active plugin.', '2meet-data-optimizer' ) ) );
+		}
+		$lines = array();
+		foreach ( $restored as $r ) {
+			$lines[] = sprintf(
+				'%s/%s (%d fields%s%s)',
+				$r['entity_type'],
+				$r['group'],
+				$r['fields'],
+				$r['skipped'] ? ', skipped: ' . implode( ',', $r['skipped'] ) : '',
+				$r['native'] ? ', left on native meta (newer data there): ' . implode( ',', $r['native'] ) : ''
+			);
+		}
+		return self::wrap(
+			'wpdo_orphaned_entity_groups',
+			self::fail(
+				__( 'WPDO entity groups restored from stored definitions', '2meet-data-optimizer' ),
+				sprintf(
+					/* translators: %s: list of entity/group names */
+					__( 'No active plugin registers these groups, so their stored definitions were re-applied to keep the flat-table data readable. Reactivate the owning plugin, or write the data back to native meta before removing it: %s', '2meet-data-optimizer' ),
+					implode( '; ', $lines )
+				),
+				'recommended'
+			)
+		);
+	}
+
 	/**
 	 * Wrap a raw check result with required Site Health envelope fields.
 	 *