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/upscale_test.go

@@ -0,0 +1,69 @@
+package assets
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestUpscalePNGUsesBackend(t *testing.T) {
+	// A fake backend binary on PATH so look() resolves it.
+	binDir := t.TempDir()
+	fake := filepath.Join(binDir, "upscayl-bin")
+	if err := os.WriteFile(fake, []byte("#!/bin/sh\n"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	t.Setenv("PATH", binDir)
+
+	// Stub runner: emulate `-i in -o out -s scale` by copying in->out.
+	orig := runner
+	defer func() { runner = orig }()
+	var gotScale string
+	runner = func(dir string, env []string, name string, args ...string) ([]byte, error) {
+		var in, out string
+		for i := 0; i < len(args)-1; i++ {
+			switch args[i] {
+			case "-i":
+				in = args[i+1]
+			case "-o":
+				out = args[i+1]
+			case "-s":
+				gotScale = args[i+1]
+			}
+		}
+		data, err := os.ReadFile(in)
+		if err != nil {
+			return nil, err
+		}
+		return nil, os.WriteFile(out, data, 0o644)
+	}
+
+	dir := t.TempDir()
+	src := filepath.Join(dir, "tex.png")
+	if err := os.WriteFile(src, []byte("pngdata"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	var stdout, stderr bytes.Buffer
+	if code := runUpscale([]string{"--scale", "2", dir}, &stdout, &stderr); code != exitOK {
+		t.Fatalf("upscale exit = %d\n%s", code, stderr.String())
+	}
+	if gotScale != "2" {
+		t.Fatalf("scale passed to backend = %q, want 2", gotScale)
+	}
+	if data, _ := os.ReadFile(src); string(data) != "pngdata" {
+		t.Fatalf("upscaled file content = %q, want the backend output", data)
+	}
+}
+
+func TestUpscaleNoBackendFailsClosed(t *testing.T) {
+	t.Setenv("PATH", t.TempDir()) // empty PATH: no backend resolvable
+	dir := t.TempDir()
+	if err := os.WriteFile(filepath.Join(dir, "tex.png"), []byte("x"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	var stdout, stderr bytes.Buffer
+	if code := runUpscale([]string{dir}, &stdout, &stderr); code != exitTool {
+		t.Fatalf("no-backend exit = %d, want %d", code, exitTool)
+	}
+}