Auto-reply: smarter chunking breaks

src/auto-reply/chunk.ts

@@ -0,0 +1,48 @@
+// Utilities for splitting outbound text into platform-sized chunks without
+// unintentionally breaking on newlines. Using [\s\S] keeps newlines inside
+// the chunk so messages are only split when they truly exceed the limit.
+
+export function chunkText(text: string, limit: number): string[] {
+  if (!text) return [];
+  if (limit <= 0) return [text];
+  if (text.length <= limit) return [text];
+
+  const chunks: string[] = [];
+  let remaining = text;
+
+  while (remaining.length > limit) {
+    const window = remaining.slice(0, limit);
+
+    // 1) Prefer a newline break inside the window.
+    let breakIdx = window.lastIndexOf("\n");
+
+    // 2) Otherwise prefer the last whitespace (word boundary) inside the window.
+    if (breakIdx <= 0) {
+      for (let i = window.length - 1; i >= 0; i--) {
+        if (/\s/.test(window[i])) {
+          breakIdx = i;
+          break;
+        }
+      }
+    }
+
+    // 3) Fallback: hard break exactly at the limit.
+    if (breakIdx <= 0) breakIdx = limit;
+
+    const rawChunk = remaining.slice(0, breakIdx);
+    const chunk = rawChunk.trimEnd();
+    if (chunk.length > 0) {
+      chunks.push(chunk);
+    }
+
+    // If we broke on whitespace/newline, skip that separator; for hard breaks keep it.
+    const brokeOnSeparator =
+      breakIdx < remaining.length && /\s/.test(remaining[breakIdx]);
+    const nextStart = Math.min(remaining.length, breakIdx + (brokeOnSeparator ? 1 : 0));
+    remaining = remaining.slice(nextStart).trimStart();
+  }
+
+  if (remaining.length) chunks.push(remaining);
+
+  return chunks;
+}