chore(lint): burn down remaining warnings to zero

src/tools/builtin/audio-transcribe.ts

@@ -71,7 +71,11 @@ function validateInput(args: AudioTranscribeArgs): { valid: boolean; error?: str
   }
 
   if (hasUrl) {
-    const urlValidation = validateUrl(args.url!);
+    const url = args.url;
+    if (!url) {
+      return { valid: false, error: 'URL is required when using url mode' };
+    }
+    const urlValidation = validateUrl(url);
     if (!urlValidation.valid) {
       return urlValidation;
     }
@@ -153,7 +157,7 @@ export function createAudioTranscribeTool(audioConfig?: AudioTranscriptionConfig
             'audio/mp4': 'm4a',
             'audio/x-m4a': 'm4a',
           };
-          const ext = extMap[args.mime_type!] || 'bin';
+          const ext = extMap[args.mime_type ?? ''] || 'bin';
           filename = `audio.${ext}`;
 
           const mimeType = args.mime_type ?? 'audio/wav';