fix(extension): harden chat and target tab lifecycle

extension/chat-format.js

@@ -29,5 +29,41 @@
         return tokens;
     }
 
-    root.KoalaSyncChatFormat = Object.freeze({ escapeChatHtml, formatChatText, tokenizeChatText });
+    function splitChatText(value, maxCodePoints = 500, maxChunks = 10) {
+        if (!Number.isInteger(maxCodePoints) || maxCodePoints < 1 || !Number.isInteger(maxChunks) || maxChunks < 1) {
+            throw new TypeError('Chat chunk limits must be positive integers');
+        }
+        let remaining = [...String(value ?? '').trim()];
+        if (remaining.length === 0) return [];
+        if (remaining.length > maxCodePoints * maxChunks) {
+            throw new RangeError('Chat composer text exceeds the chunk limit');
+        }
+
+        const chunks = [];
+        while (remaining.length > 0) {
+            if (remaining.length <= maxCodePoints) {
+                chunks.push(remaining.join('').trim());
+                break;
+            }
+
+            const remainingSlots = maxChunks - chunks.length;
+            const minimumSplit = Math.max(1, remaining.length - (remainingSlots - 1) * maxCodePoints);
+            let splitAt = maxCodePoints;
+            for (let index = maxCodePoints - 1; index >= minimumSplit; index--) {
+                if (/\s/u.test(remaining[index])) {
+                    splitAt = index;
+                    break;
+                }
+            }
+
+            const chunk = remaining.slice(0, splitAt).join('').trim();
+            remaining = remaining.slice(splitAt);
+            while (remaining.length > 0 && /\s/u.test(remaining[0])) remaining.shift();
+            if (chunk) chunks.push(chunk);
+        }
+
+        return chunks;
+    }
+
+    root.KoalaSyncChatFormat = Object.freeze({ escapeChatHtml, formatChatText, tokenizeChatText, splitChatText });
 })(globalThis);