perf(2meet-data-optimizer): keep cached routed counts across unrelated post meta writes

- cached counts followed posts' last_changed, which WordPress moves on any
  post meta write; themes write meta on page views (on dev36 Blocksy saved a
  dynamic-CSS descriptor for each listing a crawler visited), so the cache
  was invalidated every few seconds and keyword/filter searches recounted
- counts now follow their own last_changed group (tmdo_posts), bumped on
  clean_post_cache (post saved or deleted; hooked in every mode) and on flat
  writes through the Hook Bus, plus terms' last_changed; a routed search reads
  no unmanaged meta
- Verify: PostQueryRouterFoundRowsTest (unrelated meta write keeps the count,
  save or flat write recounts), integration 588, unit 703, phpcs, stan;
  dev36 front-end
- PR: PR-117 (2.3 acceptance)

tests/integration/PostQueryRouterFoundRowsTest.php

@@ -128,7 +128,10 @@ class PostQueryRouterFoundRowsTest extends TestCase {
 		$wpdb->query( 'UPDATE `' . self::TABLE . '` SET fr_price = 5 WHERE post_id = 2' );
 		$this->assertSame( '2', $wpdb->get_var( $router->found_posts_query( 'SELECT FOUND_ROWS()', $query ) ), 'cached' );
 
-		wp_cache_set_posts_last_changed();
+		wp_cache_set_posts_last_changed(); // Any post meta write, e.g. a theme's CSS descriptor on a page view.
+		$this->assertSame( '2', $wpdb->get_var( $router->found_posts_query( 'SELECT FOUND_ROWS()', $query ) ), 'still cached' );
+
+		TMDO_Post_Query_Router::bump_count_version(); // A post saved, or a managed key written.
 		$this->assertSame( '1', $wpdb->get_var( $router->found_posts_query( 'SELECT FOUND_ROWS()', $query ) ), 'recounted' );
 	}
 
@@ -153,7 +156,7 @@ class PostQueryRouterFoundRowsTest extends TestCase {
 		$this->assertSame( '2', $count( '1' ), 'one cached count serves every exclusion list; 1 does not match' );
 		$this->assertSame( '1', $count( '2' ) );
 
-		wp_cache_set_posts_last_changed();
+		TMDO_Post_Query_Router::bump_count_version();
 		$this->assertSame( '0', $count( '2' ), 'recounted' );
 	}
 
@@ -203,6 +206,7 @@ class PostQueryRouterFoundRowsTest extends TestCase {
 	public function test_flat_writes_and_deletes_move_posts_last_changed(): void {
 		$GLOBALS['_wp_current_filter'] = 'update_post_metadata';
 		$before                        = wp_cache_get_last_changed( 'posts' );
+		$version                       = wp_cache_get_last_changed( TMDO_Post_Query_Router::COUNT_VERSION_GROUP );
 		WPDO_Hook_Bus::intercept_update( null, 1, 'fr_price', '11', '' );
 		$after_write = wp_cache_get_last_changed( 'posts' );
 
@@ -211,6 +215,7 @@ class PostQueryRouterFoundRowsTest extends TestCase {
 
 		$this->assertNotSame( $before, $after_write );
 		$this->assertNotSame( $after_write, wp_cache_get_last_changed( 'posts' ) );
+		$this->assertNotSame( $version, wp_cache_get_last_changed( TMDO_Post_Query_Router::COUNT_VERSION_GROUP ), 'routed counts follow flat writes' );
 	}
 
 	// ── flat-first: a filtered search ordered by a flat column ─────────────