harden ffmpeg pipeline failure handling and stream mapping

internal/audio/convert/convert_test.go

@@ -1,6 +1,8 @@
 package convert
 
 import (
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -59,3 +61,43 @@ func TestBuildFFmpegArgsNoCoverForOpus(t *testing.T) {
 		t.Fatalf("unexpected cover map args=%s", joined)
 	}
 }
+
+func TestConvertKeepsSourceWhenRenameFails(t *testing.T) {
+	tmp := t.TempDir()
+	in := filepath.Join(tmp, "song.flac")
+	if err := os.WriteFile(in, []byte("src"), 0o644); err != nil {
+		t.Fatalf("write input: %v", err)
+	}
+
+	fakeBin := filepath.Join(tmp, "bin")
+	if err := os.MkdirAll(fakeBin, 0o755); err != nil {
+		t.Fatalf("mkdir bin: %v", err)
+	}
+	fakeFFmpeg := filepath.Join(fakeBin, "ffmpeg")
+	script := "#!/bin/sh\nout=\"\"\nfor arg in \"$@\"; do out=\"$arg\"; done\n: > \"$out\"\n"
+	if err := os.WriteFile(fakeFFmpeg, []byte(script), 0o755); err != nil {
+		t.Fatalf("write fake ffmpeg: %v", err)
+	}
+	t.Setenv("PATH", fakeBin)
+
+	finalPath := strings.TrimSuffix(in, filepath.Ext(in)) + ".m4a"
+	if err := os.Mkdir(finalPath, 0o755); err != nil {
+		t.Fatalf("mkdir final path: %v", err)
+	}
+
+	cfg := config.ConversionConfig{Enabled: true, Codec: "ALAC"}
+	out, err := Convert(in, cfg)
+	if err == nil {
+		t.Fatalf("expected rename failure")
+	}
+	if out != in {
+		t.Fatalf("returned path = %q, want %q", out, in)
+	}
+	if _, statErr := os.Stat(in); statErr != nil {
+		t.Fatalf("expected source to remain, stat err=%v", statErr)
+	}
+	tmpPath := finalPath + ".tmp.m4a"
+	if _, statErr := os.Stat(tmpPath); !os.IsNotExist(statErr) {
+		t.Fatalf("expected temp output cleanup, stat err=%v", statErr)
+	}
+}