fix(desktop): detect WebP and AVI in RIFF magic-byte sniffing

packages/desktop/packages/shared/src/utils/__tests__/binary-detection.test.ts

@@ -29,6 +29,17 @@ const MINIMAL_PNG = Buffer.from(
   'base64'
 );
 
+// RIFF containers share the "RIFF" prefix; bytes 8-11 carry the actual form tag.
+const riffBuffer = (form: string) =>
+  Buffer.concat([
+    Buffer.from([0x52, 0x49, 0x46, 0x46]), // "RIFF"
+    Buffer.from([0x24, 0x00, 0x00, 0x00]), // chunk size (non-zero, like a real file)
+    Buffer.from(form, 'ascii'), // form tag at bytes 8-11
+    Buffer.alloc(16),
+  ]);
+const MINIMAL_WEBP = riffBuffer('WEBP');
+const MINIMAL_WAV = riffBuffer('WAVE');
+
 // Large PNG-like binary: PNG magic + binary junk with null bytes (>= 256 base64 chars, >= 128 decoded bytes)
 const LARGE_PNG_BINARY = (() => {
   const buf = Buffer.alloc(300);
@@ -382,6 +393,14 @@ describe('detectExtensionFromMagic', () => {
   test('returns empty for tiny buffer', () => {
     expect(detectExtensionFromMagic(Buffer.from([0x89]))).toBe('');
   });
+
+  test('detects WebP from the RIFF form tag, not as WAV', () => {
+    expect(detectExtensionFromMagic(MINIMAL_WEBP)).toBe('.webp');
+  });
+
+  test('still detects WAV from the RIFF/WAVE form tag', () => {
+    expect(detectExtensionFromMagic(MINIMAL_WAV)).toBe('.wav');
+  });
 });
 
 // ============================================================

packages/desktop/packages/shared/src/utils/binary-detection.ts

@@ -32,7 +32,6 @@ const MAGIC_SIGNATURES: Array<{ bytes: number[]; ext: string }> = [
   { bytes: [0x42, 0x4D], ext: '.bmp' },                        // BM
   { bytes: [0x49, 0x44, 0x33], ext: '.mp3' },                  // ID3 (MP3 with ID3 tag)
   { bytes: [0xFF, 0xFB], ext: '.mp3' },                        // MP3 frame sync
-  { bytes: [0x52, 0x49, 0x46, 0x46], ext: '.wav' },           // RIFF (WAV container)
   { bytes: [0x4F, 0x67, 0x67, 0x53], ext: '.ogg' },           // OggS
   { bytes: [0x66, 0x4C, 0x61, 0x43], ext: '.flac' },          // fLaC
 ];
@@ -118,6 +117,23 @@ export function looksLikeBinary(buffer: Buffer): boolean {
 export function detectExtensionFromMagic(buffer: Buffer): string {
   if (buffer.length < 8) return '';
 
+  // RIFF is a shared container (WAV, WebP, AVI); the four-character form tag at
+  // bytes 8-11 is what actually distinguishes them, so the "RIFF" prefix alone
+  // is ambiguous and must not be assumed to be WAV.
+  if (
+    buffer.length >= 12 &&
+    buffer[0] === 0x52 &&
+    buffer[1] === 0x49 &&
+    buffer[2] === 0x46 &&
+    buffer[3] === 0x46
+  ) {
+    const form = buffer.toString('ascii', 8, 12);
+    if (form === 'WEBP') return '.webp';
+    if (form === 'AVI ') return '.avi';
+    if (form === 'WAVE') return '.wav';
+    return '';
+  }
+
   for (const sig of MAGIC_SIGNATURES) {
     if (sig.bytes.every((byte, i) => buffer[i] === byte)) {
       return sig.ext;