Make installed banger self-contained

Fix the misleading make install path where banger and bangerd still depended on a repo checkout for Firecracker, guest artifacts, image builds, and the SSH key.

Replace repo-root inference with an explicit runtime bundle model: resolve a runtime_dir from env/config/install layout, derive concrete artifact paths from it, and update the daemon, CLI, and image-build flow to use those paths. Keep repo_root only as an explicit compatibility alias instead of auto-detecting it.

Teach customize.sh to run from a read-only bundled runtime tree while writing transient state under XDG/BANGER_STATE_DIR, and make make install copy the runtime assets into PREFIX/lib/banger so installed binaries stay usable outside the repo.

Validate with go test ./..., make build, bash -n customize.sh, and make install DESTDIR=/tmp/banger-install PREFIX=/usr. An out-of-repo installed-binary smoke test was attempted, but this sandbox blocked bangerd from binding its Unix socket (setsockopt: operation not permitted).

internal/config/config.go

@@ -12,8 +12,14 @@ import (
 )
 
 type fileConfig struct {
+	RuntimeDir         string `toml:"runtime_dir"`
 	RepoRoot           string `toml:"repo_root"`
+	FirecrackerBin     string `toml:"firecracker_bin"`
+	SSHKeyPath         string `toml:"ssh_key_path"`
+	NamegenPath        string `toml:"namegen_path"`
+	CustomizeScript    string `toml:"customize_script"`
 	DefaultImageName   string `toml:"default_image_name"`
+	DefaultRootfs      string `toml:"default_rootfs"`
 	DefaultBaseRootfs  string `toml:"default_base_rootfs"`
 	DefaultKernel      string `toml:"default_kernel"`
 	DefaultInitrd      string `toml:"default_initrd"`
@@ -30,7 +36,6 @@ type fileConfig struct {
 
 func Load(layout paths.Layout) (model.DaemonConfig, error) {
 	cfg := model.DaemonConfig{
-		RepoRoot:            paths.DetectRepoRoot(),
 		AutoStopStaleAfter:  0,
 		StatsPollInterval:   model.DefaultStatsPollInterval,
 		MetricsPollInterval: model.DefaultMetricsPollInterval,
@@ -40,39 +45,45 @@ func Load(layout paths.Layout) (model.DaemonConfig, error) {
 		DefaultDNS:          model.DefaultDNS,
 		DefaultImageName:    "default",
 	}
-	if cfg.RepoRoot != "" {
-		cfg.DefaultBaseRootfs = filepath.Join(cfg.RepoRoot, "rootfs.ext4")
-		cfg.DefaultKernel = filepath.Join(cfg.RepoRoot, "wtf/root/boot/vmlinux-6.8.0-94-generic")
-		cfg.DefaultInitrd = filepath.Join(cfg.RepoRoot, "wtf/root/boot/initrd.img-6.8.0-94-generic")
-		cfg.DefaultModulesDir = filepath.Join(cfg.RepoRoot, "wtf/root/lib/modules/6.8.0-94-generic")
-		cfg.DefaultPackagesFile = filepath.Join(cfg.RepoRoot, "packages.apt")
-	}
 
 	path := filepath.Join(layout.ConfigDir, "config.toml")
 	info, err := os.Stat(path)
-	if err != nil {
-		if os.IsNotExist(err) {
-			return cfg, nil
-		}
-		return cfg, err
-	}
-	if info.IsDir() {
-		return cfg, nil
-	}
-	data, err := os.ReadFile(path)
-	if err != nil {
-		return cfg, err
-	}
 	var file fileConfig
-	if err := toml.Unmarshal(data, &file); err != nil {
-		return cfg, err
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return cfg, err
+		}
+	} else if !info.IsDir() {
+		data, err := os.ReadFile(path)
+		if err != nil {
+			return cfg, err
+		}
+		if err := toml.Unmarshal(data, &file); err != nil {
+			return cfg, err
+		}
 	}
-	if file.RepoRoot != "" {
-		cfg.RepoRoot = file.RepoRoot
+
+	cfg.RuntimeDir = paths.ResolveRuntimeDir(file.RuntimeDir, file.RepoRoot)
+	applyRuntimeDefaults(&cfg)
+
+	if file.FirecrackerBin != "" {
+		cfg.FirecrackerBin = file.FirecrackerBin
+	}
+	if file.SSHKeyPath != "" {
+		cfg.SSHKeyPath = file.SSHKeyPath
+	}
+	if file.NamegenPath != "" {
+		cfg.NamegenPath = file.NamegenPath
+	}
+	if file.CustomizeScript != "" {
+		cfg.CustomizeScript = file.CustomizeScript
 	}
 	if file.DefaultImageName != "" {
 		cfg.DefaultImageName = file.DefaultImageName
 	}
+	if file.DefaultRootfs != "" {
+		cfg.DefaultRootfs = file.DefaultRootfs
+	}
 	if file.DefaultBaseRootfs != "" {
 		cfg.DefaultBaseRootfs = file.DefaultBaseRootfs
 	}
@@ -123,3 +134,48 @@ func Load(layout paths.Layout) (model.DaemonConfig, error) {
 	}
 	return cfg, nil
 }
+
+func applyRuntimeDefaults(cfg *model.DaemonConfig) {
+	if cfg.RuntimeDir == "" {
+		return
+	}
+	cfg.FirecrackerBin = defaultRuntimePath(cfg.FirecrackerBin, cfg.RuntimeDir, "firecracker")
+	cfg.SSHKeyPath = defaultRuntimePath(cfg.SSHKeyPath, cfg.RuntimeDir, "id_ed25519")
+	cfg.NamegenPath = defaultRuntimePath(cfg.NamegenPath, cfg.RuntimeDir, "namegen")
+	cfg.CustomizeScript = defaultRuntimePath(cfg.CustomizeScript, cfg.RuntimeDir, "customize.sh")
+	cfg.DefaultKernel = defaultRuntimePath(cfg.DefaultKernel, cfg.RuntimeDir, "wtf/root/boot/vmlinux-6.8.0-94-generic")
+	cfg.DefaultInitrd = defaultRuntimePath(cfg.DefaultInitrd, cfg.RuntimeDir, "wtf/root/boot/initrd.img-6.8.0-94-generic")
+	cfg.DefaultModulesDir = defaultRuntimePath(cfg.DefaultModulesDir, cfg.RuntimeDir, "wtf/root/lib/modules/6.8.0-94-generic")
+	cfg.DefaultPackagesFile = defaultRuntimePath(cfg.DefaultPackagesFile, cfg.RuntimeDir, "packages.apt")
+	if cfg.DefaultRootfs == "" {
+		cfg.DefaultRootfs = firstExistingRuntimePath(
+			filepath.Join(cfg.RuntimeDir, "rootfs-docker.ext4"),
+			filepath.Join(cfg.RuntimeDir, "rootfs.ext4"),
+		)
+	}
+	if cfg.DefaultBaseRootfs == "" {
+		cfg.DefaultBaseRootfs = firstExistingRuntimePath(
+			filepath.Join(cfg.RuntimeDir, "rootfs.ext4"),
+			cfg.DefaultRootfs,
+		)
+	}
+}
+
+func defaultRuntimePath(current, runtimeDir, relative string) string {
+	if current != "" {
+		return current
+	}
+	return filepath.Join(runtimeDir, relative)
+}
+
+func firstExistingRuntimePath(paths ...string) string {
+	for _, candidate := range paths {
+		if candidate == "" {
+			continue
+		}
+		if _, err := os.Stat(candidate); err == nil {
+			return candidate
+		}
+	}
+	return ""
+}