fix: decode/sanitize Slack filenames, add debug logging to transcribeSong

- Decode URI components and replace spaces with hyphens in audio filenames
- Add detailed logging around fal.storage.upload and fal-ai/whisper calls
  to diagnose Bad Request errors (logs filename, size, audioUrl, error)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: sweetmantech

src/content/__tests__/selectAttachedAudioClip.test.ts

@@ -85,6 +85,23 @@ describe("selectAttachedAudioClip", () => {
     expect(result.songTitle).toBe("my-track");
   });
 
+  it("decodes URL-encoded filenames from Slack URLs", async () => {
+    vi.mocked(transcribeSong).mockResolvedValue({
+      title: "Singin in the Rain 2",
+      fullLyrics: "",
+      segments: [],
+    });
+    vi.mocked(analyzeClips).mockResolvedValue([]);
+
+    const result = await selectAttachedAudioClip({
+      audioUrl: "https://blob.vercel-storage.com/content-attachments/audio/1774985247995-Singin%20in%20the%20Rain%202.mp3",
+      lipsync: false,
+    });
+
+    expect(result.songFilename).toBe("1774985247995-Singin-in-the-Rain-2.mp3");
+    expect(result.songTitle).toBe("1774985247995-Singin-in-the-Rain-2");
+  });
+
   it("transcribes the downloaded audio", async () => {
     vi.mocked(transcribeSong).mockResolvedValue({
       title: "song",

src/content/selectAttachedAudioClip.ts

@@ -30,9 +30,9 @@ export async function selectAttachedAudioClip({
   const arrayBuffer = await response.arrayBuffer();
   const songBuffer = Buffer.from(arrayBuffer);
 
-  // Derive filename from URL
+  // Derive filename from URL (decode %20, replace spaces for fal.ai compat)
   const urlPath = new URL(audioUrl).pathname;
-  const songFilename = urlPath.split("/").pop() ?? "attached-audio.mp3";
+  const songFilename = decodeURIComponent(urlPath.split("/").pop() ?? "attached-audio.mp3").replace(/\s+/g, "-");
   const songTitle = songFilename.replace(/\.(mp3|wav|m4a|ogg|aac)$/i, "");
 
   logStep("Attached audio downloaded", { songTitle, sizeBytes: songBuffer.byteLength });

src/content/transcribeSong.ts

@@ -25,22 +25,52 @@ export async function transcribeSong(
   songBuffer: Buffer,
   songFilename: string,
 ): Promise<SongLyrics> {
-  logger.log("Transcribing song", { filename: songFilename });
+  logger.log("Transcribing song", {
+    filename: songFilename,
+    bufferSize: songBuffer.byteLength,
+  });
 
   // Upload audio to fal storage
   const file = new File([songBuffer], songFilename, { type: "audio/mpeg" });
-  const audioUrl = await fal.storage.upload(file);
+  logger.log("Uploading audio to fal storage", {
+    fileName: file.name,
+    fileSize: file.size,
+    fileType: file.type,
+  });
+
+  let audioUrl: string;
+  try {
+    audioUrl = await fal.storage.upload(file);
+    logger.log("Audio uploaded to fal storage", { audioUrl });
+  } catch (uploadError) {
+    logger.log("fal.storage.upload failed", {
+      error: String(uploadError),
+      message: (uploadError as Error).message,
+    });
+    throw uploadError;
+  }
 
   // Transcribe with Whisper
-  const result = await fal.subscribe("fal-ai/whisper" as string, {
-    input: {
-      audio_url: audioUrl,
-      task: "transcribe",
-      chunk_level: "word",
-      language: "en",
-    },
-    logs: true,
-  });
+  let result;
+  try {
+    result = await fal.subscribe("fal-ai/whisper" as string, {
+      input: {
+        audio_url: audioUrl,
+        task: "transcribe",
+        chunk_level: "word",
+        language: "en",
+      },
+      logs: true,
+    });
+  } catch (whisperError) {
+    logger.log("fal-ai/whisper failed", {
+      error: String(whisperError),
+      message: (whisperError as Error).message,
+      audioUrl,
+      filename: songFilename,
+    });
+    throw whisperError;
+  }
 
   const data = result.data as unknown as {
     text?: string;