feat(2meet-data-optimizer): sample drift daily and record the result

- TMDO_Drift_Check::cron_tick() runs on the existing wpdo_daily_health_check event (no new schedule to add or clear): every entity type whose flat tables are written (dual_write or higher) is checked on 500 random entities per group, and the outcome replaces the recorded status, so a group found drifting leaves the router that day.
- Verify: DriftCheckTest cron cases (RED: method / hook missing); dev36 with all four entities in dual_write: one tick over 22 groups in 10 s, 0 drift, status option restored.
- PR: PR-073

tests/integration/DriftCheckTest.php

@@ -181,6 +181,45 @@ class DriftCheckTest extends TestCase {
 		$this->assertFalse( TMDO_Cache_Orchestrator::get_row( 'user', 2, 'dc_grp' ) );
 	}
 
+	// ── cron_tick() (2.2 PR-073) ────────────────────────────────────────────
+
+	private static function set_modes( ?array $modes ): void {
+		$cache = ( new ReflectionClass( WPDO_Mode_Manager::class ) )->getProperty( 'cache' );
+		$cache->setAccessible( true );
+		$cache->setValue( null, $modes );
+	}
+
+	public function test_the_daily_tick_samples_entities_that_write_to_flat(): void {
+		self::set_modes( array( 'post' => 'disabled', 'user' => 'dual_write', 'term' => 'disabled', 'comment' => 'disabled' ) );
+		try {
+			TMDO_Drift_Check::cron_tick();
+		} finally {
+			self::set_modes( null );
+		}
+
+		$status = get_option( TMDO_Drift_Check::OPTION );
+		$this->assertSame( TMDO_Drift_Check::CRON_SAMPLE, $status['user']['dc_grp']['sample'] );
+		$this->assertSame( 2, $status['user']['dc_grp']['diff'], 'the sample covers all 7 fixture users' );
+		$this->assertArrayNotHasKey( 'post', $status );
+	}
+
+	public function test_the_daily_tick_skips_entities_that_do_not_write_to_flat(): void {
+		self::set_modes( array( 'post' => 'disabled', 'user' => 'disabled', 'term' => 'disabled', 'comment' => 'disabled' ) );
+		try {
+			TMDO_Drift_Check::cron_tick();
+		} finally {
+			self::set_modes( null );
+		}
+
+		$this->assertFalse( get_option( TMDO_Drift_Check::OPTION ) );
+	}
+
+	public function test_the_daily_tick_runs_on_the_daily_health_check_hook(): void {
+		$source = (string) file_get_contents( WPDO_PLUGIN_DIR . 'includes/class-tmdo-core.php' );
+
+		$this->assertStringContainsString( "add_action( 'wpdo_daily_health_check', array( 'TMDO_Drift_Check', 'cron_tick' ) );", $source );
+	}
+
 	public function test_rejects_an_unknown_group(): void {
 		$this->expectException( InvalidArgumentException::class );
 		TMDO_Drift_Check::run( 'user', 'no_such_group' );