From b95b98b536551a38b27c893ffa55842911e7f6b5 Mon Sep 17 00:00:00 2001
From: Sukhendu Sekhar Guria <sukhendu.guria@rtcamp.com>
Date: Wed, 6 May 2026 15:26:30 +0530
Subject: [PATCH] Heartbeat: Expose post lock window to JS to prevent
 background tab race

---
 src/js/_enqueues/wp/heartbeat.js | 23 ++++++++++++++++++++---
 src/wp-admin/includes/misc.php   |  5 ++++-
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/src/js/_enqueues/wp/heartbeat.js b/src/js/_enqueues/wp/heartbeat.js
index 65635177d9f66..a286a9ecee826 100644
--- a/src/js/_enqueues/wp/heartbeat.js
+++ b/src/js/_enqueues/wp/heartbeat.js
@@ -100,7 +100,12 @@
 
 				// Timer that keeps track of how long needs to be waited before connecting to
 				// the server again.
-				beatTimer: 0
+				beatTimer: 0,
+
+				// Post lock window in milliseconds. Synced from PHP via heartbeat_settings.
+				// Used to calculate the background tab heartbeat interval.
+				// Default matches the wp_check_post_lock_window default of 150 seconds.
+				postLockWindow: 150000
 			};
 
 		/**
@@ -112,7 +117,7 @@
 		 * @return {void}
 		 */
 		function initialize() {
-			var options, hidden, visibilityState, visibilitychange;
+			var options, hidden, visibilityState, visibilitychange, postLockWindow;
 
 			if ( typeof window.pagenow === 'string' ) {
 				settings.screenId = window.pagenow;
@@ -172,6 +177,14 @@
 				if ( options.suspension === 'disable' ) {
 					settings.suspendEnabled = false;
 				}
+
+				if ( options.post_lock_window ) {
+					postLockWindow = parseInt( options.post_lock_window, 10 );
+
+					if ( postLockWindow > 0 ) {
+						settings.postLockWindow = postLockWindow * 1000;
+					}
+				}
 			}
 
 			// Convert to milliseconds.
@@ -509,7 +522,11 @@
 			}
 
 			if ( ! settings.hasFocus ) {
-				interval = 120000; // 120 seconds. Post locks expire after 150 seconds.
+				// Fire 30 seconds before the post lock window expires so backgrounded
+				// tabs always refresh the lock in time. For the default 150s window this
+				// equals 120s, preserving existing behaviour. Floored at 5s for very
+				// short custom windows.
+				interval = Math.max( 5000, settings.postLockWindow - 30000 );
 			} else if ( settings.countdown > 0 && settings.tempInterval ) {
 				interval = settings.tempInterval;
 				settings.countdown--;
diff --git a/src/wp-admin/includes/misc.php b/src/wp-admin/includes/misc.php
index 3724684ffd428..1b223143f5947 100644
--- a/src/wp-admin/includes/misc.php
+++ b/src/wp-admin/includes/misc.php
@@ -1334,7 +1334,7 @@ function wp_refresh_heartbeat_nonces( $response ) {
 }
 
 /**
- * Disables suspension of Heartbeat on the Add/Edit Post screens.
+ * Disables suspension of Heartbeat and sets post lock data on the Add/Edit Post screens.
  *
  * @since 3.8.0
  *
@@ -1348,6 +1348,9 @@ function wp_heartbeat_set_suspension( $settings ) {
 
 	if ( 'post.php' === $pagenow || 'post-new.php' === $pagenow ) {
 		$settings['suspension'] = 'disable';
+
+		/** This filter is documented in wp-admin/includes/ajax-actions.php */
+		$settings['post_lock_window'] = apply_filters( 'wp_check_post_lock_window', 150 );
 	}
 
 	return $settings;