From a212a8575ab4db91126d5089944edeea41602762 Mon Sep 17 00:00:00 2001
From: Mustafa Bharmal <mjbharmal2002@gmail.com>
Date: Wed, 13 May 2026 21:54:51 +0530
Subject: [PATCH 1/2] Block Library: Fix Tabs block losing added tabs on editor
 reopen

---
 packages/block-library/src/tab-panels/edit.js | 11 ++++-
 packages/block-library/src/tabs/edit.js       | 44 ++++++-------------
 2 files changed, 23 insertions(+), 32 deletions(-)

diff --git a/packages/block-library/src/tab-panels/edit.js b/packages/block-library/src/tab-panels/edit.js
index 01422a9cc38791..d191ed320becd8 100644
--- a/packages/block-library/src/tab-panels/edit.js
+++ b/packages/block-library/src/tab-panels/edit.js
@@ -7,6 +7,7 @@ import {
 	store as blockEditorStore,
 } from '@wordpress/block-editor';
 import { useSelect } from '@wordpress/data';
+import { __ } from '@wordpress/i18n';
 
 /**
  * Internal dependencies
@@ -14,7 +15,15 @@ import { useSelect } from '@wordpress/data';
 import AddTabToolbarControl from '../tab-panel/add-tab-toolbar-control';
 import RemoveTabToolbarControl from '../tab-panel/remove-tab-toolbar-control';
 
-const TAB_PANELS_TEMPLATE = [ [ 'core/tab-panel', {} ] ];
+/**
+ * Initial template applied only when the block is first inserted (i.e. when
+ * inner blocks are empty). templateLock is false, so this is never applied to
+ * existing blocks that already have tab panels saved.
+ */
+const TAB_PANELS_TEMPLATE = [
+	[ 'core/tab-panel', { label: __( 'Tab' ) } ],
+	[ 'core/tab-panel', { label: __( 'Tab' ) } ],
+];
 
 export default function Edit( { clientId } ) {
 	const blockProps = useBlockProps();
diff --git a/packages/block-library/src/tabs/edit.js b/packages/block-library/src/tabs/edit.js
index cfb3fd102a001e..2bf64eaa031477 100644
--- a/packages/block-library/src/tabs/edit.js
+++ b/packages/block-library/src/tabs/edit.js
@@ -9,7 +9,6 @@ import {
 } from '@wordpress/block-editor';
 import { useSelect } from '@wordpress/data';
 import { useMemo, useEffect } from '@wordpress/element';
-import { __ } from '@wordpress/i18n';
 
 /**
  * Internal dependencies
@@ -19,36 +18,19 @@ import useTabListSync from './use-tab-list-sync';
 
 const EMPTY_ARRAY = [];
 
-const TABS_TEMPLATE = [
-	[
-		'core/tab-list',
-		{},
-		[
-			[ 'core/tab', {} ],
-			[ 'core/tab', {} ],
-		],
-	],
-	[
-		'core/tab-panels',
-		{},
-		[
-			[
-				'core/tab-panel',
-				{
-					label: __( 'Tab' ),
-				},
-				[ [ 'core/paragraph' ] ],
-			],
-			[
-				'core/tab-panel',
-				{
-					label: __( 'Tab' ),
-				},
-				[ [ 'core/paragraph' ] ],
-			],
-		],
-	],
-];
+/**
+ * Only the two structural child blocks are specified here — without inner
+ * block entries for core/tab-list or core/tab-panels.
+ *
+ * If inner blocks were included in this template, `synchronizeBlocksWithTemplate`
+ * (called whenever templateLock === 'all') would recurse into the containers and
+ * truncate them to the template count, causing data loss when a saved block with
+ * more than two tabs is re-opened in the editor.
+ *
+ * Initial tab/panel creation is delegated to the tab-panels template in
+ * tab-panels/edit.js (templateLock: false, applied only when empty).
+ */
+const TABS_TEMPLATE = [ [ 'core/tab-list' ], [ 'core/tab-panels' ] ];
 
 function Edit( { clientId, attributes, setAttributes } ) {
 	const { anchor, activeTabIndex, editorActiveTabIndex } = attributes;

From 0414a34f644574dc89cbeb473c25eca1aed4d1d3 Mon Sep 17 00:00:00 2001
From: Mustafa Bharmal <mjbharmal2002@gmail.com>
Date: Thu, 14 May 2026 00:02:11 +0530
Subject: [PATCH 2/2] Block Library: Add default template for tab-list block

---
 packages/block-library/src/tab-list/edit.js | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/packages/block-library/src/tab-list/edit.js b/packages/block-library/src/tab-list/edit.js
index 607150eb89fa8e..7122686537ebfe 100644
--- a/packages/block-library/src/tab-list/edit.js
+++ b/packages/block-library/src/tab-list/edit.js
@@ -14,6 +14,8 @@ import { useSelect } from '@wordpress/data';
 import AddTabToolbarControl from '../tab-panel/add-tab-toolbar-control';
 import RemoveTabToolbarControl from '../tab-panel/remove-tab-toolbar-control';
 
+const TAB_LIST_TEMPLATE = [ [ 'core/tab' ], [ 'core/tab' ] ];
+
 function Edit( { clientId } ) {
 	const tabsClientId = useSelect(
 		( select ) =>
@@ -26,6 +28,7 @@ function Edit( { clientId } ) {
 	const innerBlocksProps = useInnerBlocksProps( blockProps, {
 		allowedBlocks: [ 'core/tab' ],
 		orientation: 'horizontal',
+		template: TAB_LIST_TEMPLATE,
 		templateLock: false,
 		renderAppender: false,
 	} );