fix(discord): cap lines per message

src/discord/chunk.test.ts

@@ -0,0 +1,70 @@
+import { describe, expect, it } from "vitest";
+
+import { chunkDiscordText } from "./chunk.js";
+
+function countLines(text: string) {
+  return text.split("\n").length;
+}
+
+function hasBalancedFences(chunk: string) {
+  let open: { markerChar: string; markerLen: number } | null = null;
+  for (const line of chunk.split("\n")) {
+    const match = line.match(/^( {0,3})(`{3,}|~{3,})(.*)$/);
+    if (!match) continue;
+    const marker = match[2];
+    if (!open) {
+      open = { markerChar: marker[0], markerLen: marker.length };
+      continue;
+    }
+    if (open.markerChar === marker[0] && marker.length >= open.markerLen) {
+      open = null;
+    }
+  }
+  return open === null;
+}
+
+describe("chunkDiscordText", () => {
+  it("splits tall messages even when under 2000 chars", () => {
+    const text = Array.from({ length: 45 }, (_, i) => `line-${i + 1}`).join(
+      "\n",
+    );
+    expect(text.length).toBeLessThan(2000);
+
+    const chunks = chunkDiscordText(text, { maxChars: 2000, maxLines: 20 });
+    expect(chunks.length).toBeGreaterThan(1);
+    for (const chunk of chunks) {
+      expect(countLines(chunk)).toBeLessThanOrEqual(20);
+    }
+  });
+
+  it("keeps fenced code blocks balanced across chunks", () => {
+    const body = Array.from(
+      { length: 30 },
+      (_, i) => `console.log(${i});`,
+    ).join("\n");
+    const text = `Here is code:\n\n\`\`\`js\n${body}\n\`\`\`\n\nDone.`;
+
+    const chunks = chunkDiscordText(text, { maxChars: 2000, maxLines: 10 });
+    expect(chunks.length).toBeGreaterThan(1);
+
+    for (const chunk of chunks) {
+      expect(hasBalancedFences(chunk)).toBe(true);
+      expect(chunk.length).toBeLessThanOrEqual(2000);
+    }
+
+    expect(chunks[0]).toContain("```js");
+    expect(chunks.at(-1)).toContain("Done.");
+  });
+
+  it("reserves space for closing fences when chunking", () => {
+    const body = "a".repeat(120);
+    const text = `\`\`\`txt\n${body}\n\`\`\``;
+
+    const chunks = chunkDiscordText(text, { maxChars: 50, maxLines: 50 });
+    expect(chunks.length).toBeGreaterThan(1);
+    for (const chunk of chunks) {
+      expect(chunk.length).toBeLessThanOrEqual(50);
+      expect(hasBalancedFences(chunk)).toBe(true);
+    }
+  });
+});