feat(chat): add in-page overlay

extension/chat-format.js

@@ -0,0 +1,33 @@
+(function exposeChatFormat(root) {
+    function escapeChatHtml(value) {
+        return String(value ?? '')
+            .replace(/&/g, '&')
+            .replace(/</g, '&lt;')
+            .replace(/>/g, '&gt;')
+            .replace(/"/g, '&quot;')
+            .replace(/'/g, '&#039;');
+    }
+
+    function formatChatText(value) {
+        return escapeChatHtml(value)
+            .replace(/\*\*([^*\n]+)\*\*/g, '<strong>$1</strong>')
+            .replace(/\*([^*\n]+)\*/g, '<em>$1</em>');
+    }
+
+    function tokenizeChatText(value) {
+        const text = String(value ?? '');
+        const tokens = [];
+        const pattern = /\*\*([^*\n]+)\*\*|\*([^*\n]+)\*/g;
+        let cursor = 0;
+        let match;
+        while ((match = pattern.exec(text)) !== null) {
+            if (match.index > cursor) tokens.push({ type: 'text', text: text.slice(cursor, match.index) });
+            tokens.push({ type: match[1] !== undefined ? 'strong' : 'em', text: match[1] ?? match[2] });
+            cursor = pattern.lastIndex;
+        }
+        if (cursor < text.length) tokens.push({ type: 'text', text: text.slice(cursor) });
+        return tokens;
+    }
+
+    root.KoalaSyncChatFormat = Object.freeze({ escapeChatHtml, formatChatText, tokenizeChatText });
+})(globalThis);