fix(2meet-data-optimizer): do not recreate a deleted entity's flat row

- Deleting a post / user / term / comment drops its flat row in the adapter delete hook, then WordPress deletes each meta row; sync_from_native upserted NULL for each and brought the row back (512 orphan rows on dev36). With no native value it now only clears the column on an existing row
- Verify: tests/live/run.php resync (25/25, entity deletes in dual_write and shadow_read leave no flat row); mut.php T8 flat_row NO-ROW; integration 516
- PR: PR-057b

includes/engine/class-tmdo-hook-bus.php

@@ -201,7 +201,8 @@ final class TMDO_Hook_Bus {
 	 * (NULL when native has no row). Runs in dual_write / shadow_read only,
 	 * after WP wrote native, so flat always ends up equal to native — also
 	 * when WP skipped or refused the write, and when an earlier direct SQL
-	 * write had left flat stale.
+	 * write had left flat stale. A NULL never creates a row: deleting an
+	 * entity drops its flat row before WP deletes the meta rows one by one.
 	 *
 	 * @param string $type       Entity type.
 	 * @param int    $object_id  Entity ID.
@@ -222,7 +223,9 @@ final class TMDO_Hook_Bus {
 
 		$before = self::maybe_read_before_value( $type, $object_id, $meta_key, $field_def, $op );
 		$native = self::native_first_value( $type, $object_id, $meta_key );
-		$result = self::perform_upsert( $type, $object_id, $meta_key, null === $native ? null : maybe_unserialize( $native ), $field_def );
+		$result = null === $native
+			? self::clear_column( $type, $object_id, $meta_key, $field_def )
+			: self::perform_upsert( $type, $object_id, $meta_key, maybe_unserialize( $native ), $field_def );
 
 		if ( 'delete' === $op ) {
 			do_action( 'wpdo_after_delete', $type, $object_id, $meta_key, $meta_value, $result, $delete_all, $before );
@@ -522,6 +525,34 @@ final class TMDO_Hook_Bus {
 		return 'flat';
 	}
 
+	/**
+	 * Set a flat column to NULL on the entity's existing row; never insert one.
+	 *
+	 * @param string               $type      Entity type.
+	 * @param int                  $entity_id Entity ID.
+	 * @param string               $meta_key  Meta key.
+	 * @param array<string, mixed> $field_def Registered field.
+	 * @return bool|null Null when there is no adapter or table.
+	 */
+	private static function clear_column( string $type, int $entity_id, string $meta_key, array $field_def ): ?bool {
+		global $wpdb;
+
+		$adapter = TMDO_Entity_Registry::get_adapter( $type );
+		$table   = TMDO_Schema_Manager::get_table_name( $type, $field_def['group'] );
+		if ( ! $adapter || ! TMDO_Schema_Manager::table_exists( $table ) ) {
+			return null;
+		}
+
+		$col = TMDO_Schema_Manager::sanitize_column_name( $meta_key );
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$result = $wpdb->update( $table, array( $col => null ), array( $adapter->get_entity_id_column() => $entity_id ) );
+
+		TMDO_Cache_Orchestrator::invalidate( $type, $entity_id, $field_def['group'] );
+		self::touch_posts_last_changed( $type );
+
+		return false !== $result;
+	}
+
 	/**
 	 * 執行 Upsert 操作
 	 */

tests/integration/HookBusIntegrationTest.php

@@ -256,6 +256,24 @@ class HookBusIntegrationTest extends TestCase {
 		);
 	}
 
+	/**
+	 * Deleting an entity drops its flat row first (adapter delete hook), then
+	 * WordPress deletes each meta row; syncing those deletions must not bring
+	 * the row back as all NULL.
+	 */
+	public function test_sync_of_a_deleted_key_does_not_recreate_a_missing_row(): void {
+		global $wpdb;
+		self::set_user_mode( WPDO_Mode_Manager::MODE_DUAL_WRITE );
+
+		$this->with_usermeta(
+			function () use ( $wpdb ) {
+				WPDO_Hook_Bus::sync_from_native( 'user', 31, 'first_name', 'Gone', 'delete' );
+
+				$this->assertSame( '0', $wpdb->get_var( 'SELECT COUNT(*) FROM `' . self::FLAT_TABLE . '` WHERE user_id = 31' ) );
+			}
+		);
+	}
+
 	/**
 	 * Run $fn with a native usermeta table, dropped afterwards.
 	 */

tests/live/suites/resync.php

@@ -110,3 +110,29 @@ foreach ( array( 'dual_write', 'shadow_read' ) as $tmdo_live_mode ) {
 		);
 	}
 }
+
+TMDO_Live::test(
+	'deleting an entity leaves no flat row behind (dual_write and shadow_read)',
+	static function () {
+		require_once ABSPATH . 'wp-admin/includes/user.php';
+		$deleters = array(
+			'user'    => static fn( int $id ) => wp_delete_user( $id ),
+			'post'    => static fn( int $id ) => wp_delete_post( $id, true ),
+			'term'    => static fn( int $id ) => wp_delete_term( $id, 'hp_listing_category' ),
+			'comment' => static fn( int $id ) => wp_delete_comment( $id, true ),
+		);
+		foreach ( array( 'dual_write', 'shadow_read' ) as $mode ) {
+			foreach ( tmdo_live_resync_cases() as $label => $case ) {
+				list( $type, $key, $make, $pt ) = $case;
+				TMDO_Live_Fixtures::field( $type, $key, $pt );
+				TMDO_Live_Fixtures::use_modes( array( $type => $mode ) );
+				$id = $make();
+				update_metadata( $type, $id, $key, '41' );
+
+				$deleters[ $type ]( $id );
+
+				tmdo_live_assert_same( 'NO-ROW', TMDO_Live_Fixtures::flat( $type, $id, $key, $pt ), "{$mode} {$label}: flat row after delete" );
+			}
+		}
+	}
+);