fix(cli): beats --json answers with no track when the composition has no music (#6690)

* fix(cli): beats --json answers with no track when the composition has no music

* fix(cli): drop a comment the name already says

packages/cli/src/commands/beats.test.ts

@@ -44,7 +44,7 @@ function project(name: string, bpm: number | null, seconds = 12): string {
   return dir;
 }
 
-async function runBeats(dir: string): Promise<{ exitCode: number; out: string }> {
+async function runBeats(dir: string, json = true): Promise<{ exitCode: number; out: string }> {
   const command = (await import("./beats.js")).default as unknown as {
     run: (context: { args: Record<string, unknown> }) => Promise<void>;
   };
@@ -54,7 +54,7 @@ async function runBeats(dir: string): Promise<{ exitCode: number; out: string }>
   const error = vi.spyOn(console, "error").mockImplementation(capture);
   let exitCode = 0;
   try {
-    await command.run({ args: { dir, json: true } });
+    await command.run({ args: { dir, json } });
   } catch (thrown) {
     exitCode = (thrown as { result?: { exitCode?: number } }).result?.exitCode ?? -1;
   } finally {
@@ -105,6 +105,23 @@ describe.skipIf(!canDecode)("hyperframes beats", () => {
     expect(out).not.toContain("hyperframes audio");
   });
 
+  it("answers --json with no track, not a failure, when the composition has no music", async () => {
+    const dir = project("no-track", 120);
+    writeFileSync(join(dir, "index.html"), `<div data-composition-id="main"></div>`);
+    const { exitCode, out } = await runBeats(dir);
+    expect(exitCode).toBe(0);
+    expect(JSON.parse(out)).toEqual({ ok: true, track: null, file: null, count: 0, bpm: null });
+    expect(existsSync(join(dir, "beats"))).toBe(false);
+  });
+
+  it("still tells a person with no music track how to mark one", async () => {
+    const dir = project("no-track-person", 120);
+    writeFileSync(join(dir, "index.html"), `<div data-composition-id="main"></div>`);
+    const { exitCode, out } = await runBeats(dir, false);
+    expect(exitCode).toBe(1);
+    expect(out).toMatch(/No music track found/);
+  });
+
   it("writes nothing for a track with no steady beat", async () => {
     const dir = project("silent", null);
     const { exitCode, out } = await runBeats(dir);

packages/cli/src/commands/beats.ts

@@ -50,16 +50,15 @@ function findMusicSrc(html: string): string | null {
   return findMusicAudioSrc(document.toString());
 }
 
-/** Locate the music track + its on-disk audio, or fail with a clear message. */
-function resolveMusicTarget(project: ProjectDir): { rel: string; audioPath: string } {
+const NO_MUSIC_TRACK =
+  'No music track found. Add data-timeline-role="music" to the <audio> element, or to a ' +
+  '<video data-has-audio="true"> whose own sound is the music ' +
+  "(or give it an id like music/bgm/soundtrack).";
+
+/** Locate the music track + its on-disk audio: null when the composition has none, or fail with a clear message. */
+function resolveMusicTarget(project: ProjectDir): { rel: string; audioPath: string } | null {
   const src = findMusicSrc(readFileSync(project.indexPath, "utf-8"));
-  if (!src) {
-    fail(
-      'No music track found. Add data-timeline-role="music" to the <audio> element, or to a ' +
-        '<video data-has-audio="true"> whose own sound is the music ' +
-        "(or give it an id like music/bgm/soundtrack).",
-    );
-  }
+  if (!src) return null;
   const rel = audioRelPathForSrc(src); // same derivation the Studio uses
   if (!rel) fail(`Cannot derive a beat-file path for music src: ${src}`);
   const audioPath = resolveWithinProject(project.dir, rel);
@@ -68,6 +67,11 @@ function resolveMusicTarget(project: ProjectDir): { rel: string; audioPath: stri
   return { rel, audioPath };
 }
 
+function answerNoTrack(json: boolean): void {
+  if (!json) fail(NO_MUSIC_TRACK);
+  console.log(JSON.stringify({ ok: true, track: null, file: null, count: 0, bpm: null }, null, 2));
+}
+
 async function decode(audioPath: string): Promise<AudioSignal> {
   try {
     const decoded = await decodeAudio(audioPath);
@@ -112,7 +116,9 @@ export default defineCommand({
       );
     }
     const project = resolveProject(args.dir);
-    const { rel, audioPath } = resolveMusicTarget(project);
+    const target = resolveMusicTarget(project);
+    if (!target) return answerNoTrack(Boolean(args.json));
+    const { rel, audioPath } = target;
     if (!args.json) console.log(c.dim(`Analyzing ${rel}…`));
 
     const result = await analyzeMusicFromSignal(await decode(audioPath));