feat: download audio file attachments instead of transcribing them

Voice messages (Discord IsVoiceMessage flag or attachment with duration)
are still transcribed via Whisper. Regular audio file attachments (WAV,
MP3, etc.) are now downloaded to disk and the path is passed to the
agent, matching image attachment behavior.

src/channels/discord.ts

@@ -26,20 +26,23 @@ const ATTACHMENTS_DIR = path.join(DATA_DIR, 'attachments');
 const TRANSCRIPTION_CACHE_DIR = path.join(CACHE_DIR, 'transcriptions');
 
 /**
- * Download a Discord image attachment to local disk.
+ * Download a Discord attachment to local disk.
  * Returns the absolute path to the saved file.
  */
-async function downloadImage(att: Attachment): Promise<string> {
+async function downloadAttachment(
+  att: Attachment,
+  defaultExt = '.bin',
+): Promise<string> {
   const res = await fetch(att.url);
   if (!res.ok) throw new Error(`Download failed: ${res.status}`);
   const buffer = Buffer.from(await res.arrayBuffer());
 
   fs.mkdirSync(ATTACHMENTS_DIR, { recursive: true });
-  const ext = path.extname(att.name || 'image.png') || '.png';
+  const ext = path.extname(att.name || `file${defaultExt}`) || defaultExt;
   const filename = `${Date.now()}-${att.id}${ext}`;
   const filePath = path.join(ATTACHMENTS_DIR, filename);
   fs.writeFileSync(filePath, buffer);
-  logger.info({ file: filename, size: buffer.length }, 'Image downloaded');
+  logger.info({ file: filename, size: buffer.length }, 'Attachment downloaded');
   return filePath;
 }
 
@@ -254,25 +257,40 @@ export class DiscordChannel implements Channel {
         }
       }
 
-      // Handle attachments — transcribe audio, placeholder for others
+      // Handle attachments — transcribe voice messages, download files
+      const isVoiceMessage = message.flags.has(MessageFlags.IsVoiceMessage);
       if (message.attachments.size > 0) {
         const attachmentDescriptions = await Promise.all(
           [...message.attachments.values()].map(async (att) => {
             const contentType = att.contentType || '';
-            if (contentType.startsWith('audio/')) {
+            // Voice messages → transcribe; regular audio files → download
+            if (
+              contentType.startsWith('audio/') &&
+              (isVoiceMessage || att.duration != null)
+            ) {
               return transcribeAudio(att);
-            } else if (contentType.startsWith('image/')) {
+            } else if (
+              contentType.startsWith('audio/') ||
+              contentType.startsWith('image/')
+            ) {
               try {
-                const imgPath = await downloadImage(att);
-                return `[Image: ${imgPath}]`;
+                const filePath = await downloadAttachment(
+                  att,
+                  contentType.startsWith('image/') ? '.png' : '.wav',
+                );
+                const label = contentType.startsWith('image/')
+                  ? 'Image'
+                  : 'Audio';
+                return `[${label}: ${filePath}]`;
               } catch (err) {
-                logger.error({ err, file: att.name }, 'Image download failed');
-                return `[Image: ${att.name || 'image'} (download failed)]`;
+                logger.error(
+                  { err, file: att.name },
+                  'Attachment download failed',
+                );
+                return `[File: ${att.name || 'file'} (download failed)]`;
               }
             } else if (contentType.startsWith('video/')) {
               return `[Video: ${att.name || 'video'}]`;
-            } else if (contentType.startsWith('audio/')) {
-              return `[Audio: ${att.name || 'audio'}]`;
             } else if (
               contentType.startsWith('text/') ||
               /\.(txt|md|json|csv|log|xml|yaml|yml|toml|ini|cfg|conf|sh|bash|zsh|py|js|ts|jsx|tsx|html|css|sql|rs|go|java|c|cpp|h|hpp|rb|php|swift|kt|scala|r|lua|pl|ex|exs|hs|ml|clj|dart|v|zig|nim|ps1|bat|cmd|mjs|cjs)$/i.test(