refactor(2meet-data-optimizer): handle admin form posts before the page renders

- the main page's form handlers move unchanged from render_page() to
  handle_post(), hooked on load-{page}: inside render_page() the admin
  header was already sent, so their wp_safe_redirect() calls could not work
- the setup wizard's step 4 snapshot post moves to handle_snapshot_post() on
  its load hook; a failure redirects with snap_failed=1 for the notice
- Verify: unit 701, integration 577, phpcs, stan; dev36 load hook handles a
  posted reset and redirects before output
- PR: PR-097

admin/class-tmdo-admin.php

@@ -89,13 +89,16 @@ class TMDO_Admin {
 	 * Register the admin menu page under Tools.
 	 */
 	public static function register_menu(): void {
-		add_management_page(
+		$hook_suffix = add_management_page(
 			__( 'WP Data Optimizer', '2meet-data-optimizer' ),
 			__( 'WP Data Optimizer', '2meet-data-optimizer' ),
 			'manage_options',
 			self::MENU_SLUG,
 			array( __CLASS__, 'render_page' )
 		);
+		if ( $hook_suffix ) {
+			add_action( 'load-' . $hook_suffix, array( __CLASS__, 'handle_post' ) );
+		}
 	}
 
 	/**
@@ -326,9 +329,10 @@ class TMDO_Admin {
 	}
 
 	/**
-	 * Render the admin page.
+	 * Handle the page's form posts on load-{page}, before any output, so their
+	 * redirects work (inside render_page() the admin header was already sent).
 	 */
-	public static function render_page(): void {
+	public static function handle_post(): void {
 		if ( ! TMDO_Capability::current_user_can_admin() ) {
 			return;
 		}
@@ -752,6 +756,15 @@ class TMDO_Admin {
 			);
 			exit;
 		}
+	}
+
+	/**
+	 * Render the admin page.
+	 */
+	public static function render_page(): void {
+		if ( ! TMDO_Capability::current_user_can_admin() ) {
+			return;
+		}
 
 		$tabs = array(
 			'dashboard'             => __( '儀表板', '2meet-data-optimizer' ),
@@ -774,7 +787,7 @@ class TMDO_Admin {
 			'hivepress'             => __( 'HivePress 整合', '2meet-data-optimizer' ),
 		);
 
-		$tab = sanitize_key( wp_unslash( $_GET['tab'] ?? 'dashboard' ) );
+		$tab = sanitize_key( wp_unslash( $_GET['tab'] ?? 'dashboard' ) ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended -- tab navigation, no state change.
 		// v2.11.8: legacy tabs removed — redirect bookmarks to current main maintenance entry.
 		if ( in_array( $tab, array( 'sop', 'migration' ), true ) ) {
 			$tab = 'entity-bridge';

admin/class-tmdo-setup-wizard.php

@@ -106,7 +106,7 @@ class TMDO_Setup_Wizard {
 	 * @return void
 	 */
 	public static function register_menu_page(): void {
-		add_submenu_page(
+		$hook_suffix = add_submenu_page(
 			'tools.php',
 			__( 'WPDO 設定嚮導', '2meet-data-optimizer' ),
 			__( 'WPDO 設定嚮導', '2meet-data-optimizer' ),
@@ -114,6 +114,33 @@ class TMDO_Setup_Wizard {
 			'wpdo-setup-wizard',
 			array( __CLASS__, 'render_page' )
 		);
+		if ( $hook_suffix ) {
+			add_action( 'load-' . $hook_suffix, array( __CLASS__, 'handle_snapshot_post' ) );
+		}
+	}
+
+	/**
+	 * Step 4 baseline snapshot (POST + nonce, prevents Referer leak — v3.3.x
+	 * P1-6b hardening), handled on load-{page} so the redirect runs before any
+	 * output.
+	 *
+	 * @return void
+	 */
+	public static function handle_snapshot_post(): void {
+		if ( ! isset( $_POST['wpdo_take_snapshot'] ) || ! TMDO_Capability::current_user_can_admin() || ! class_exists( 'TMDO_Snapshot_Manager' ) ) {
+			return;
+		}
+		check_admin_referer( self::NONCE_NAME );
+		$result = TMDO_Snapshot_Manager::create(
+			'manual',
+			array(),
+			array(
+				'notes'          => 'wizard_baseline',
+				'retention_days' => 365,
+			)
+		);
+		wp_safe_redirect( admin_url( 'tools.php?page=wpdo-setup-wizard&step=4&' . ( empty( $result['ok'] ) ? 'snap_failed=1' : 'snap_done=1' ) ) );
+		exit;
 	}
 
 	/**
@@ -356,20 +383,8 @@ class TMDO_Setup_Wizard {
 				</p>
 			</form>
 			<?php
-			// Take snapshot if action requested (POST + nonce, prevents Referer leak — v3.3.x P1-6b hardening).
-			if ( isset( $_POST['wpdo_take_snapshot'] ) && check_admin_referer( self::NONCE_NAME ) && class_exists( 'TMDO_Snapshot_Manager' ) ) {
-				$result = TMDO_Snapshot_Manager::create(
-					'manual',
-					array(),
-					array(
-						'notes'          => 'wizard_baseline',
-						'retention_days' => 365,
-					)
-				);
-				if ( ! empty( $result['ok'] ) ) {
-					wp_safe_redirect( admin_url( 'tools.php?page=wpdo-setup-wizard&step=4&snap_done=1' ) );
-					exit;
-				}
+			// The snapshot itself is taken in handle_snapshot_post(), before any output.
+			if ( isset( $_GET['snap_failed'] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
 				echo '<div class="notice notice-error"><p>' . esc_html__( 'Snapshot 建立失敗，請查日誌。', '2meet-data-optimizer' ) . '</p></div>';
 			}
 			?>