fix: extract audio URL from Fal TTS response

Fal returns audio in result.audio.url for TTS models, but the media URL
extraction chain didn't check for this field. Add audio URL extraction,
isAudioModel detection, and audio-specific output handling that returns
base64-encoded audio with type "audio".

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/api/generate/providers/fal.ts

@@ -473,6 +473,8 @@ export async function generateWithFalQueue(
         mediaUrl = result.glb.url;
       } else if (result.video && result.video.url) {
         mediaUrl = result.video.url;
+      } else if (result.audio && result.audio.url) {
+        mediaUrl = result.audio.url;
       } else if (result.images && Array.isArray(result.images) && result.images.length > 0) {
         mediaUrl = result.images[0].url;
       } else if (result.image && result.image.url) {
@@ -508,6 +510,7 @@ export async function generateWithFalQueue(
 
       const is3DModel = input.model.capabilities.some(c => c.includes("3d"));
       const isVideoModel = input.model.capabilities.some(c => c.includes("video"));
+      const isAudioModel = input.model.capabilities.some(c => c.includes("audio"));
 
       // For 3D models, return URL directly (GLB files are binary — don't base64 encode)
       if (is3DModel) {
@@ -524,6 +527,22 @@ export async function generateWithFalQueue(
         };
       }
 
+      // For audio models, always base64 encode (audio files are small)
+      if (isAudioModel) {
+        const audioContentType = mediaResponse.headers.get("content-type") || "audio/mpeg";
+        const audioBuffer = await mediaResponse.arrayBuffer();
+        const audioBase64 = Buffer.from(audioBuffer).toString("base64");
+        console.log(`[API:${requestId}] SUCCESS - Returning audio`);
+        return {
+          success: true,
+          outputs: [{
+            type: "audio",
+            data: `data:${audioContentType};base64,${audioBase64}`,
+            url: mediaUrl,
+          }],
+        };
+      }
+
       const contentType = mediaResponse.headers.get("content-type") || (isVideoModel ? "video/mp4" : "image/png");
       const isVideo = contentType.startsWith("video/");