perf: debounce message sync in ResponseMessage during streaming

The JSON.stringify sync runs for every visible message on each token,
not just the one streaming. Debounce to 50ms while streaming, sync
immediately when done.

Author: Algorithm5838

src/lib/components/chat/Messages/ResponseMessage.svelte

@@ -120,12 +120,26 @@
 	export let selectedModels = [];
 
 	let message: MessageType = JSON.parse(JSON.stringify(history.messages[messageId]));
-	$: if (history.messages) {
+	let messageSyncTimer: ReturnType<typeof setTimeout>;
+
+	function syncMessage() {
 		if (JSON.stringify(message) !== JSON.stringify(history.messages[messageId])) {
 			message = JSON.parse(JSON.stringify(history.messages[messageId]));
 		}
 	}
 
+	$: if (history.messages) {
+		if (history.messages[messageId]?.done) {
+			// Message done, sync now
+			clearTimeout(messageSyncTimer);
+			syncMessage();
+		} else {
+			// Debounce during streaming
+			clearTimeout(messageSyncTimer);
+			messageSyncTimer = setTimeout(syncMessage, 50);
+		}
+	}
+
 	export let siblings;
 
 	export let setInputText: Function = () => {};
@@ -589,6 +603,8 @@
 	});
 
 	onDestroy(() => {
+		clearTimeout(messageSyncTimer);
+
 		if (buttonsContainerElement) {
 			buttonsContainerElement.removeEventListener('wheel', buttonsWheelHandler);
 		}