fix: merge chat history to prevent message loss

Author: Algorithm5838

backend/open_webui/models/chats.py

@@ -133,6 +133,7 @@ class ChatFileModel(BaseModel):
 class ChatForm(BaseModel):
     chat: dict
     folder_id: str | None = None
+    deleted_message_ids: list[str] | None = None
 
 
 class ChatImportForm(ChatForm):
@@ -478,6 +479,68 @@ def get_unresolved_parent_ids(messages_map: dict) -> set[str]:
             if msg.get('parentId') and msg['parentId'] not in messages_map
         }
 
+    @staticmethod
+    def _expand_deleted_ids(messages_map: dict, deleted_ids, protected_ids=()) -> set[str]:
+        """Grow an explicit deletion set to its orphaned descendants, keeping any
+        node that reappears in ``protected_ids`` (reparented children survive).
+        """
+        dead = set(deleted_ids)
+        if not dead:
+            return dead
+        changed = True
+        while changed:
+            changed = False
+            for message_id, message in messages_map.items():
+                if message_id in dead or message_id in protected_ids:
+                    continue
+                if message.get('parentId') in dead:
+                    dead.add(message_id)
+                    changed = True
+        # Intersect so unknown/already-gone ids in deleted_ids don't leak out.
+        return dead & set(messages_map)
+
+    @staticmethod
+    def merge_history(existing_history: dict, incoming_history: dict, deleted_message_ids=None) -> dict:
+        """Merge an incoming history onto the stored one without inferring deletions.
+
+        Messages absent from the push are kept — only ``deleted_message_ids`` and
+        their orphaned descendants are removed — so a stale client can't drop a
+        message it never saw. Blob counterpart to ``reconcile_messages_by_chat_id``.
+        """
+        existing = (existing_history or {}).get('messages') or {}
+        incoming = (incoming_history or {}).get('messages') or {}
+        merged = {**existing, **incoming}
+
+        for message_id in ChatTable._expand_deleted_ids(
+            merged, deleted_message_ids or [], protected_ids=incoming
+        ):
+            merged.pop(message_id, None)
+
+        # Rebuild childrenIds from parentId so concurrent branches stay reachable
+        # (display only; the model context walks parentId, not childrenIds).
+        for message in merged.values():
+            message['childrenIds'] = [
+                child_id for child_id in (message.get('childrenIds') or []) if child_id in merged
+            ]
+        for message_id, message in merged.items():
+            parent_id = message.get('parentId')
+            if parent_id in merged and message_id not in merged[parent_id]['childrenIds']:
+                merged[parent_id]['childrenIds'].append(message_id)
+
+        # Keep the push's currentId; fall back only if it was pruned.
+        current_id = (incoming_history or {}).get('currentId')
+        if current_id not in merged:
+            fallback = (existing_history or {}).get('currentId')
+            current_id = fallback if fallback in merged else None
+
+        # Preserve any other history keys from the push (fall back to existing),
+        # then override messages/currentId with the merged result.
+        return {
+            **(incoming_history or existing_history or {}),
+            'messages': merged,
+            'currentId': current_id,
+        }
+
     async def backfill_messages_by_chat_id(self, chat_id: str, user_id: str, messages: dict[str, dict]) -> None:
         """Write messages to the ``chat_message`` table so future lookups
         use the fast path.  Errors are logged but never raised.
@@ -496,22 +559,28 @@ async def backfill_messages_by_chat_id(self, chat_id: str, user_id: str, message
                 log.warning('Backfill failed for message %s in chat %s: %s', message_id, chat_id, e)
 
     async def reconcile_messages_by_chat_id(
-        self, chat_id: str, user_id: str, messages: dict[str, dict]
+        self, chat_id: str, user_id: str, messages: dict[str, dict], deleted_message_ids=None
     ) -> None:
         """Sync ``chat_message`` rows with the committed JSON blob.
 
-        Upserts current messages via ``backfill_messages_by_chat_id``
-        and deletes orphaned rows whose message_id no longer appears
-        in the blob.  Best-effort: errors are logged but never raised.
+        Upserts the pushed messages via ``backfill_messages_by_chat_id``, then
+        prunes only the IDs the client explicitly reported in ``deleted_message_ids``
+        plus their orphaned descendants. Rows merely missing from the push are never
+        inferred as deletions — otherwise a stale/lost-update save would silently drop
+        a still-valid message from the model context. Best-effort: errors are logged
+        but never raised.
         """
         try:
             await self.backfill_messages_by_chat_id(chat_id, user_id, messages)
 
-            existing_map = await ChatMessages.get_messages_map_by_chat_id(chat_id)
-            if existing_map is not None:
-                orphaned_ids = set(existing_map.keys()) - set(messages.keys())
-                if orphaned_ids:
-                    await ChatMessages.delete_message_ids_by_chat_id(chat_id, orphaned_ids)
+            if deleted_message_ids:
+                existing_map = await ChatMessages.get_messages_map_by_chat_id(chat_id)
+                if existing_map is not None:
+                    dead_ids = self._expand_deleted_ids(
+                        existing_map, deleted_message_ids, protected_ids=messages
+                    )
+                    if dead_ids:
+                        await ChatMessages.delete_message_ids_by_chat_id(chat_id, dead_ids)
         except Exception as e:
             log.warning('Failed to reconcile chat_message rows for chat %s: %s', chat_id, e)
 

backend/open_webui/routers/chats.py

@@ -968,6 +968,15 @@ async def update_chat_by_id(
     if chat:
         updated_chat = {**chat.chat, **form_data.chat}
 
+        # Merge (don't replace) history so a stale save can't clobber unseen
+        # messages; see Chats.merge_history for the full rationale.
+        if 'history' in form_data.chat:
+            updated_chat['history'] = Chats.merge_history(
+                chat.chat.get('history'),
+                form_data.chat.get('history'),
+                deleted_message_ids=form_data.deleted_message_ids,
+            )
+
         # Re-derive content from output for assistant messages so that
         # frontend edits to output items are always reflected in content.
         # serialize_output() is the single source of truth for this conversion.
@@ -982,7 +991,9 @@ async def update_chat_by_id(
         # history with potential edits, deletions, or new branches.
         messages = (updated_chat.get('history') or {}).get('messages') or {}
         if messages:
-            await Chats.reconcile_messages_by_chat_id(id, user.id, messages)
+            await Chats.reconcile_messages_by_chat_id(
+                id, user.id, messages, deleted_message_ids=form_data.deleted_message_ids
+            )
 
         return ChatResponse(**chat.model_dump())
     else:

src/lib/apis/chats/index.ts

@@ -1039,7 +1039,12 @@ export const getChatAccessGrants = async (token: string, id: string) => {
 	return res;
 };
 
-export const updateChatById = async (token: string, id: string, chat: object) => {
+export const updateChatById = async (
+	token: string,
+	id: string,
+	chat: object,
+	deletedMessageIds: string[] = []
+) => {
 	let error = null;
 
 	const res = await fetch(`${WEBUI_API_BASE_URL}/chats/${id}`, {
@@ -1050,7 +1055,9 @@ export const updateChatById = async (token: string, id: string, chat: object) =>
 			...(token && { authorization: `Bearer ${token}` })
 		},
 		body: JSON.stringify({
-			chat: chat
+			chat: chat,
+			// Only sent when the client explicitly deleted messages; absent => upsert-only (no pruning).
+			...(deletedMessageIds.length > 0 && { deleted_message_ids: deletedMessageIds })
 		})
 	})
 		.then(async (res) => {

src/lib/components/chat/Chat.svelte

@@ -409,7 +409,7 @@
 		}
 	};
 
-	const showMessage = async (message, scroll = true) => {
+	const showMessage = async (message, scroll = true, save = true) => {
 		const _chatId = JSON.parse(JSON.stringify($chatId));
 		let _messageId = JSON.parse(JSON.stringify(message.id));
 
@@ -442,7 +442,10 @@
 		await tick();
 		await tick();
 
-		saveChatHandler(_chatId, history);
+		// Callers that persist separately (e.g. deleteMessage's tombstone-carrying save) pass save=false.
+		if (save) {
+			saveChatHandler(_chatId, history);
+		}
 	};
 
 	const updateLastReadAt = (id) => {

src/lib/components/chat/Messages.svelte

@@ -164,14 +164,26 @@
 		}
 	};
 
+	// IDs explicitly deleted by the user, sent with the next save so the backend prunes
+	// the matching chat_message rows. Cleared only on a successful save (survives retry).
+	let deletedMessageIds = new Set();
+
 	const updateChat = async () => {
 		if (!$temporaryChatEnabled) {
 			history = history;
 			await tick();
-			const res = await updateChatById(localStorage.token, chatId, {
-				history: history,
-				messages: messages
-			});
+			const res = await updateChatById(
+				localStorage.token,
+				chatId,
+				{
+					history: history,
+					messages: messages
+				},
+				Array.from(deletedMessageIds)
+			);
+
+			// Reached only when the save succeeded (updateChatById throws on failure).
+			deletedMessageIds.clear();
 
 			// Refresh local message content from backend (e.g. re-derived via serialize_output)
 			if (res?.chat?.history?.messages) {
@@ -458,12 +470,18 @@
 			}
 		});
 
-		// Delete the message and its children
+		// Delete the message and its children, buffering the IDs so the next save
+		// tells the backend to prune the matching chat_message rows. Grandchildren
+		// were reparented above and are intentionally not tombstoned.
 		[messageId, ...childMessageIds].forEach((id) => {
 			delete history.messages[id];
+			deletedMessageIds.add(id);
 		});
 
-		showMessage({ id: parentMessageId }, false);
+		// Move currentId to the parent without saving, then persist once via
+		// updateChat() so the deletion travels with its deleted_message_ids.
+		showMessage({ id: parentMessageId }, false, false);
+		await updateChat();
 	};
 
 	const triggerScroll = () => {