perf: reconcile markdown tokens to skip unchanged blocks

Author: Algorithm5838

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

@@ -62,6 +62,18 @@
 	let pendingUpdate = null;
 	let lastContent = '';
 	let lastParsedContent = '';
+	let lastTokens = [];
+
+	// Keep the same object for unchanged blocks so the keyed each skips re-rendering them
+	const reconcileTokens = (next) => {
+		for (let i = 0; i < next.length; i++) {
+			if (lastTokens[i] && lastTokens[i].raw === next[i].raw) {
+				next[i] = lastTokens[i];
+			}
+		}
+		lastTokens = next;
+		return next;
+	};
 
 	const parseTokens = () => {
 		if (content === lastContent) return;
@@ -71,7 +83,7 @@
 		if (processed === lastParsedContent) return;
 		lastParsedContent = processed;
 
-		tokens = marked.lexer(processed);
+		tokens = reconcileTokens(marked.lexer(processed));
 	};
 
 	const updateHandler = (content) => {