fix(lyrics): send full lyrics chunked under TeamSpeak message cap (#116)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/bot/text-chunk.test.ts

@@ -0,0 +1,67 @@
+import { describe, it, expect } from "vitest";
+import { splitTextIntoChunks } from "./text-chunk.js";
+
+const bytes = (s: string) => Buffer.byteLength(s, "utf8");
+
+describe("splitTextIntoChunks", () => {
+  it("returns a single chunk for a short string", () => {
+    const chunks = splitTextIntoChunks("hello world", 900);
+    expect(chunks).toEqual(["hello world"]);
+  });
+
+  it("splits a multi-line string longer than maxBytes into multiple chunks on line boundaries", () => {
+    const lines = Array.from({ length: 50 }, (_, i) => `line number ${i}`);
+    const text = lines.join("\n");
+    const chunks = splitTextIntoChunks(text, 60);
+
+    expect(chunks.length).toBeGreaterThan(1);
+    for (const c of chunks) {
+      expect(bytes(c)).toBeLessThanOrEqual(60);
+    }
+    // No hard-split of any line occurred, so rejoining with "\n" is lossless.
+    expect(chunks.join("\n")).toBe(text);
+  });
+
+  it("bounds by BYTES not chars: multibyte (Chinese) content stays under the cap", () => {
+    // Each Chinese char is 3 bytes in UTF-8. 40 chars/line = 120 bytes/line.
+    const lines = Array.from({ length: 10 }, () => "歌词".repeat(20));
+    const text = lines.join("\n");
+    const chunks = splitTextIntoChunks(text, 150);
+
+    expect(chunks.length).toBeGreaterThan(1);
+    for (const c of chunks) {
+      expect(bytes(c)).toBeLessThanOrEqual(150);
+    }
+    expect(chunks.join("\n")).toBe(text);
+  });
+
+  it("hard-splits a single over-long line so no chunk exceeds the cap", () => {
+    const longLine = "a".repeat(500);
+    const chunks = splitTextIntoChunks(longLine, 100);
+
+    expect(chunks.length).toBeGreaterThan(1);
+    for (const c of chunks) {
+      expect(bytes(c)).toBeLessThanOrEqual(100);
+    }
+    // Content is preserved (hard-split introduces split points, not \n).
+    expect(chunks.join("")).toBe(longLine);
+  });
+
+  it("never splits a multibyte character across a hard-split boundary", () => {
+    // 200 Chinese chars = 600 bytes on ONE line, cap 40 bytes.
+    const longLine = "歌".repeat(200);
+    const chunks = splitTextIntoChunks(longLine, 40);
+
+    for (const c of chunks) {
+      expect(bytes(c)).toBeLessThanOrEqual(40);
+      // A clean re-decode: every chunk is valid UTF-8 with no replacement char.
+      expect(c.includes("�")).toBe(false);
+    }
+    expect(chunks.join("")).toBe(longLine);
+  });
+
+  it("preserves blank lines within a single chunk", () => {
+    const text = "a\n\nb";
+    expect(splitTextIntoChunks(text, 900)).toEqual([text]);
+  });
+});