coverage: easy-wins batch across cli, system, paths, vmdns, toolingplan

Pure-Go tests for formatters, layout resolution, and validators — no
fixtures, no external processes. Targets previously-zero functions the
triage scan flagged as low-hanging fruit.

  cli          55% -> 65%
  paths        64% -> 91%
  system       65% -> 75%
  vmdns        72% -> 86%
  toolingplan  73% -> 78%

Total 52.6% -> 54.0%.

internal/paths/layout_test.go

@@ -0,0 +1,136 @@
+package paths
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestResolveUsesXDGOverrides(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("XDG_CONFIG_HOME", filepath.Join(dir, "config"))
+	t.Setenv("XDG_STATE_HOME", filepath.Join(dir, "state"))
+	t.Setenv("XDG_CACHE_HOME", filepath.Join(dir, "cache"))
+	t.Setenv("XDG_RUNTIME_DIR", filepath.Join(dir, "run"))
+
+	layout, err := Resolve()
+	if err != nil {
+		t.Fatalf("Resolve: %v", err)
+	}
+	if layout.ConfigDir != filepath.Join(dir, "config", "banger") {
+		t.Errorf("ConfigDir = %q", layout.ConfigDir)
+	}
+	if layout.StateDir != filepath.Join(dir, "state", "banger") {
+		t.Errorf("StateDir = %q", layout.StateDir)
+	}
+	if layout.CacheDir != filepath.Join(dir, "cache", "banger") {
+		t.Errorf("CacheDir = %q", layout.CacheDir)
+	}
+	if layout.RuntimeDir != filepath.Join(dir, "run", "banger") {
+		t.Errorf("RuntimeDir = %q", layout.RuntimeDir)
+	}
+	if !strings.HasSuffix(layout.SocketPath, "bangerd.sock") {
+		t.Errorf("SocketPath = %q", layout.SocketPath)
+	}
+	if !strings.HasSuffix(layout.DBPath, "state.db") {
+		t.Errorf("DBPath = %q", layout.DBPath)
+	}
+}
+
+func TestResolveFallsBackWhenRuntimeUnset(t *testing.T) {
+	t.Setenv("XDG_RUNTIME_DIR", "")
+	layout, err := Resolve()
+	if err != nil {
+		t.Fatalf("Resolve: %v", err)
+	}
+	if !strings.Contains(layout.RuntimeDir, "banger-runtime-") {
+		t.Errorf("expected fallback runtime dir, got %q", layout.RuntimeDir)
+	}
+}
+
+func TestEnsureCreatesAllDirs(t *testing.T) {
+	base := t.TempDir()
+	layout := Layout{
+		ConfigDir:   filepath.Join(base, "config"),
+		StateDir:    filepath.Join(base, "state"),
+		CacheDir:    filepath.Join(base, "cache"),
+		RuntimeDir:  filepath.Join(base, "runtime"),
+		VMsDir:      filepath.Join(base, "state/vms"),
+		ImagesDir:   filepath.Join(base, "state/images"),
+		KernelsDir:  filepath.Join(base, "state/kernels"),
+		OCICacheDir: filepath.Join(base, "cache/oci"),
+	}
+	if err := Ensure(layout); err != nil {
+		t.Fatalf("Ensure: %v", err)
+	}
+	for _, dir := range []string{
+		layout.ConfigDir,
+		layout.StateDir,
+		layout.CacheDir,
+		layout.RuntimeDir,
+		layout.VMsDir,
+		layout.ImagesDir,
+		layout.KernelsDir,
+		layout.OCICacheDir,
+	} {
+		info, err := os.Stat(dir)
+		if err != nil {
+			t.Errorf("stat %q: %v", dir, err)
+			continue
+		}
+		if !info.IsDir() {
+			t.Errorf("%q is not a directory", dir)
+		}
+	}
+
+	// Idempotent.
+	if err := Ensure(layout); err != nil {
+		t.Fatalf("Ensure (second run): %v", err)
+	}
+}
+
+func TestBangerdPathEnvOverride(t *testing.T) {
+	t.Setenv("BANGER_DAEMON_BIN", "/tmp/custom-bangerd")
+	got, err := BangerdPath()
+	if err != nil {
+		t.Fatalf("BangerdPath: %v", err)
+	}
+	if got != "/tmp/custom-bangerd" {
+		t.Errorf("got %q, want /tmp/custom-bangerd", got)
+	}
+}
+
+func TestBangerdPathFindsSiblingBinary(t *testing.T) {
+	t.Setenv("BANGER_DAEMON_BIN", "")
+
+	root := t.TempDir()
+	sibling := filepath.Join(root, "bangerd")
+	if err := os.WriteFile(sibling, []byte("#!/bin/sh\n"), 0o755); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+	original := executablePath
+	executablePath = func() (string, error) { return filepath.Join(root, "banger"), nil }
+	t.Cleanup(func() { executablePath = original })
+
+	got, err := BangerdPath()
+	if err != nil {
+		t.Fatalf("BangerdPath: %v", err)
+	}
+	if got != sibling {
+		t.Errorf("got %q, want %q", got, sibling)
+	}
+}
+
+func TestBangerdPathNotFound(t *testing.T) {
+	t.Setenv("BANGER_DAEMON_BIN", "")
+
+	root := t.TempDir()
+	original := executablePath
+	executablePath = func() (string, error) { return filepath.Join(root, "banger"), nil }
+	t.Cleanup(func() { executablePath = original })
+
+	if _, err := BangerdPath(); err == nil {
+		t.Fatal("expected error when no sibling bangerd exists")
+	}
+}