feat: Initial clean release of CHM

packages/lib/services/ai/utils/findFencedBlock.ts

@@ -0,0 +1,24 @@
+import { pregQuote } from '../../../string-utils';
+
+const fencedBlockRegex = (tag: string) =>
+	new RegExp(`\`\`\`${pregQuote(tag)}\\s*\\n([\\s\\S]*?)\\n?\`\`\``, 'gi');
+
+// Cursor=0 fallback (no selection) makes the first match win naturally.
+const findFencedBlock = (body: string, tag: string, cursorPos: number) => {
+	const re = fencedBlockRegex(tag);
+	let best: RegExpExecArray | null = null;
+	let bestDistance = Infinity;
+	let match: RegExpExecArray | null;
+	while ((match = re.exec(body)) !== null) {
+		const distance = Math.abs(match.index - cursorPos);
+		if (distance < bestDistance) {
+			bestDistance = distance;
+			best = match;
+		}
+		// Defensive against zero-width matches looping forever.
+		if (match.index === re.lastIndex) re.lastIndex++;
+	}
+	return best;
+};
+
+export default findFencedBlock;