fix(engine): fail partial audio track preparation (#2488)

packages/engine/src/services/audioMixer.test.ts

@@ -143,6 +143,61 @@ describe("processCompositionAudio", () => {
     expect(filter).toContain("[mixed]volume=3[out]");
   });
 
+  it("fails the audio result instead of silently mixing after one track preparation fails", async () => {
+    const baseDir = mkdtempSync(join(tmpdir(), "hf-audio-base-"));
+    const workDir = mkdtempSync(join(tmpdir(), "hf-audio-work-"));
+    tempDirs.push(baseDir, workDir);
+
+    writeFileSync(join(baseDir, "working.wav"), "stub");
+    writeFileSync(join(baseDir, "missing-cue.wav"), "stub");
+
+    const defaultImplementation = runFfmpegMock.getMockImplementation()!;
+    runFfmpegMock.mockImplementation(async (args: string[]) => {
+      const isMissingCuePrepare = args.includes(join(baseDir, "missing-cue.wav"));
+      return {
+        success: !isMissingCuePrepare,
+        durationMs: 1,
+        stderr: isMissingCuePrepare ? "Invalid data found when processing input" : "",
+        exitCode: isMissingCuePrepare ? 1 : 0,
+      };
+    });
+
+    const result = await processCompositionAudio(
+      [
+        {
+          id: "working",
+          src: "working.wav",
+          start: 0,
+          end: 0.5,
+          mediaStart: 0,
+          layer: 0,
+          volume: 1,
+          type: "audio",
+        },
+        {
+          id: "missing-cue",
+          src: "missing-cue.wav",
+          start: 3.859,
+          end: 4.359,
+          mediaStart: 0,
+          layer: 1,
+          volume: 1,
+          type: "audio",
+        },
+      ],
+      baseDir,
+      workDir,
+      join(baseDir, "out.m4a"),
+      5,
+    );
+    runFfmpegMock.mockImplementation(defaultImplementation);
+
+    expect(result.success).toBe(false);
+    expect(result.tracksProcessed).toBe(1);
+    expect(result.error).toMatch(/Prepare failed: missing-cue/);
+    expect(runFfmpegMock).toHaveBeenCalledTimes(2);
+  });
+
   it("uses frame-evaluated volume automation when keyframes are present", async () => {
     const baseDir = mkdtempSync(join(tmpdir(), "hf-audio-base-"));
     const workDir = mkdtempSync(join(tmpdir(), "hf-audio-work-"));

packages/engine/src/services/audioMixer.ts

@@ -625,6 +625,25 @@ export async function processCompositionAudio(
     }),
   );
 
+  // Never turn a per-track preparation failure into a successful partial mix.
+  // The producer only surfaces audio failures when `success` is false; mixing
+  // the remaining tracks made the omitted cue indistinguishable from a valid
+  // render unless someone manually audited that exact audio window.
+  if (errors.length > 0) {
+    try {
+      rmSync(workDir, { recursive: true, force: true });
+    } catch {
+      /* ignore */
+    }
+    return {
+      success: false,
+      outputPath,
+      durationMs: Date.now() - startMs,
+      tracksProcessed: tracks.length,
+      error: `Audio processing failed: ${errors.join(", ")}`,
+    };
+  }
+
   const mixResult = await mixAudioTracks(tracks, outputPath, totalDuration, signal, config);
 
   try {