perf: debounce message sync in ResponseMessage during streaming

Avoids running JSON.stringify for all visible messages on every token.

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);
 		}