From c50bc7347ac2476d867165b6d24f8e3a6631affe Mon Sep 17 00:00:00 2001
From: Alexander Zinchuk <alx.zinchuk@gmail.com>
Date: Wed, 18 Jun 2025 17:41:01 +0200
Subject: [PATCH] Messages: Fix message sending in threads (#6008)

---
 src/global/actions/api/messages.ts         | 7 ++++++-
 src/global/actions/apiUpdaters/messages.ts | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/global/actions/api/messages.ts b/src/global/actions/api/messages.ts
index 934fdcd37..037614a93 100644
--- a/src/global/actions/api/messages.ts
+++ b/src/global/actions/api/messages.ts
@@ -138,6 +138,7 @@ import {
   selectSendAs,
   selectTabState,
   selectThreadIdFromMessage,
+  selectThreadInfo,
   selectTopic,
   selectTranslationLanguage,
   selectUser,
@@ -344,7 +345,11 @@ addActionHandler('sendMessage', async (global, actions, payload): Promise<void>
   const messageReplyInfo = selectMessageReplyInfo(global, chatId!, threadId!, draftReplyInfo);
 
   const replyInfo = storyReplyInfo || messageReplyInfo;
-  const lastMessageId = selectChatLastMessageId(global, chatId!);
+
+  const threadInfo = selectThreadInfo(global, chatId!, threadId!);
+  const lastMessageId = threadId === MAIN_THREAD_ID
+    ? selectChatLastMessageId(global, chatId!) : threadInfo?.lastMessageId;
+
   const messagePriceInStars = await getPeerStarsForMessage(global, chatId!);
 
   const params: SendMessageParams = {
diff --git a/src/global/actions/apiUpdaters/messages.ts b/src/global/actions/apiUpdaters/messages.ts
index 7cd227239..d1645fc79 100644
--- a/src/global/actions/apiUpdaters/messages.ts
+++ b/src/global/actions/apiUpdaters/messages.ts
@@ -1088,6 +1088,11 @@ function updateChatLastMessage<T extends GlobalState>(
     });
   }
 
+  const threadId = selectThreadIdFromMessage(global, message);
+  global = updateThreadInfo(global, chatId, threadId, {
+    lastMessageId: message.id,
+  });
+
   const savedDialogId = selectSavedDialogIdFromMessage(global, message);
   if (savedDialogId) {
     global = updateChatLastMessageId(global, savedDialogId, message.id, 'saved');