Revert "perf: skip deep clone of message during streaming"

This reverts commit f4ae514.

Author: Algorithm5838

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

@@ -120,18 +120,9 @@
 	export let selectedModels = [];
 
 	let message: MessageType = JSON.parse(JSON.stringify(history.messages[messageId]));
-	let streaming = false;
-
 	$: if (history.messages) {
-		const source = history.messages[messageId];
-		if (source && !source.done) {
-			// During streaming: use direct reference to avoid costly serialization.
-			// All mutation controls (edit, rate, feedback) are gated behind message.done.
-			message = source;
-			streaming = true;
-		} else if (streaming || JSON.stringify(message) !== JSON.stringify(source)) {
-			message = JSON.parse(JSON.stringify(source));
-			streaming = false;
+		if (JSON.stringify(message) !== JSON.stringify(history.messages[messageId])) {
+			message = JSON.parse(JSON.stringify(history.messages[messageId]));
 		}
 	}