test(audio): ffprobe output past a cap is unreadable, not buffered (#49), red

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/adapters/audio/ffprobe_test.go

@@ -215,3 +215,22 @@ func TestFFprobeProbe_AsksOnlyForTheFieldsParseProbeReads(t *testing.T) {
 	require.GreaterOrEqual(t, se, 0, "argv: %v", args)
 	assert.Equal(t, "format=duration:stream=codec_type:stream_disposition=attached_pic", args[se+1])
 }
+
+func TestFFprobeProbe_OutputPastTheCapIsUnreadableNotBuffered(t *testing.T) {
+	// ffprobe's stdout is attacker-influenced (tags, 491 MB observed). Past the cap the
+	// probe is stopped and the file is reported as unreadable (#49).
+	bin := stub(t, `head -c 200000 /dev/zero | tr '\0' 'a'`)
+
+	_, err := (&audio.FFprobe{Bin: bin, MaxOutput: 4096}).Probe(context.Background(), "/x")
+
+	assert.ErrorIs(t, err, uploads.ErrUnreadable)
+}
+
+func TestFFprobeProbe_OutputWithinTheCapIsParsed(t *testing.T) {
+	bin := stub(t, `echo '{"streams":[{"codec_type":"audio"}],"format":{"duration":"90"}}'`)
+
+	got, err := (&audio.FFprobe{Bin: bin, MaxOutput: 4096}).Probe(context.Background(), "/x")
+
+	require.NoError(t, err)
+	assert.True(t, got.HasAudio)
+}