feat(assets): seven asset commands + Run dispatch/helpers

check-dupes, clean-dupes, check-mdl, fix-mdl, convert, upscale, compile
behind a single runner indirection, mirroring internal/depot's Run shape.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/assets/convert_test.go

@@ -0,0 +1,108 @@
+package assets
+
+import (
+	"bytes"
+	"image"
+	"image/color"
+	"image/png"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+// writeTestPNG writes a 16x16 image: top half red, bottom half blue. The size
+// and the half-way split keep every 4x4 DXT block a single flat color, so the
+// DXT1 round trip stays lossless and only the flip is under test. (A 4x4 image
+// is one mixed DXT block that magick's encoder collapses to a single color.)
+func writeTestPNG(t *testing.T, path string) {
+	t.Helper()
+	const n = 16
+	img := image.NewRGBA(image.Rect(0, 0, n, n))
+	for y := 0; y < n; y++ {
+		c := color.RGBA{255, 0, 0, 255} // red
+		if y >= n/2 {
+			c = color.RGBA{0, 0, 255, 255} // blue
+		}
+		for x := 0; x < n; x++ {
+			img.Set(x, y, c)
+		}
+	}
+	f, err := os.Create(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	if err := png.Encode(f, img); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func topRowIsBlue(t *testing.T, pngPath string) bool {
+	t.Helper()
+	f, err := os.Open(pngPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	img, err := png.Decode(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	r, _, b, _ := img.At(0, 0).RGBA()
+	return b > r // blue dominates the top-left after a flip
+}
+
+func TestConvertFlipsOnceAndRoundTrips(t *testing.T) {
+	magick := look("magick")
+	if magick == "" {
+		t.Skip("magick not on PATH")
+	}
+	dir := t.TempDir()
+	src := filepath.Join(dir, "tex.png")
+	writeTestPNG(t, src)
+
+	// Convert PNG -> DDS (in place: tex.png becomes tex.dds, original removed).
+	var out, errw bytes.Buffer
+	if code := runConvert([]string{"--to", "dds", dir}, &out, &errw); code != exitOK {
+		t.Fatalf("to-dds exit = %d\n%s", code, errw.String())
+	}
+	dds := filepath.Join(dir, "tex.dds")
+	if _, err := os.Stat(dds); err != nil {
+		t.Fatalf("dds not produced: %v", err)
+	}
+	if _, err := os.Stat(src); !os.IsNotExist(err) {
+		t.Fatal("source png was not replaced")
+	}
+
+	// Decode the DDS RAW (no extra flip) and confirm a single flip happened:
+	// the source top row was red, so the DDS top row must now be blue.
+	raw := filepath.Join(dir, "raw.png")
+	if err := exec.Command(magick, dds, raw).Run(); err != nil {
+		t.Fatalf("raw decode: %v", err)
+	}
+	if !topRowIsBlue(t, raw) {
+		t.Fatal("expected the DDS to be vertically flipped vs the source")
+	}
+
+	// Convert DDS -> PNG (another flip). Result should match the original.
+	out.Reset()
+	errw.Reset()
+	if code := runConvert([]string{"--to", "png", dir}, &out, &errw); code != exitOK {
+		t.Fatalf("to-png exit = %d\n%s", code, errw.String())
+	}
+	restored := filepath.Join(dir, "tex.png")
+	if topRowIsBlue(t, restored) {
+		t.Fatal("round trip did not restore the original orientation")
+	}
+}
+
+func TestConvertMissingBackendFailsClosed(t *testing.T) {
+	dir := t.TempDir()
+	writeTestPNG(t, filepath.Join(dir, "tex.png"))
+	var out, errw bytes.Buffer
+	code := runConvert([]string{"--backend", "/nonexistent/magick", dir}, &out, &errw)
+	if code != exitTool {
+		t.Fatalf("missing backend exit = %d, want %d", code, exitTool)
+	}
+}