vm create: auto-pull image and kernel from catalogs if missing

One-command sandbox: `banger vm run` on a fresh host now Just Works.
No prior `banger image pull` or `banger kernel pull` needed.

Changes:

- Default `default_image_name` flips from "default" to "debian-bookworm"
  so the golden image is the implicit target when `--image` is omitted.
- `CreateVM` resolves the image via a new `findOrAutoPullImage`: try
  the local store first, and on miss fall back to the embedded imagecat
  catalog + auto-pull. Emits a vm-create progress stage so the user
  sees "pulling from image catalog" in the create output.
- `resolveKernelInputs` gains context + the same pattern via
  `readOrAutoPullKernel`: try the local kernelcat, and on miss look up
  the embedded kernelcat and auto-pull. Fires whenever a bundle's
  manifest references a kernel the user hasn't pulled yet, not just
  during image pull — any CreateVM with an image that needs a kernel
  not yet local will resolve it.
- `--image` help text updated on both `vm run` and `vm create`.

Six tests cover local-hit-no-pull, auto-pull-on-miss, not-in-catalog
error propagation, and a non-ENOENT kernel read error does NOT trigger
a misleading "not in catalog" claim.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/cli/banger.go

@@ -859,7 +859,7 @@ Three modes:
 		},
 	}
 	cmd.Flags().StringVar(&name, "name", "", "vm name")
-	cmd.Flags().StringVar(&imageName, "image", "", "image name or id")
+	cmd.Flags().StringVar(&imageName, "image", "", "image name or id (defaults to config's default_image_name; auto-pulled from imagecat if missing)")
 	cmd.Flags().IntVar(&vcpu, "vcpu", model.DefaultVCPUCount, "vcpu count")
 	cmd.Flags().IntVar(&memory, "memory", model.DefaultMemoryMiB, "memory in MiB")
 	cmd.Flags().StringVar(&systemOverlaySize, "system-overlay-size", model.FormatSizeBytes(model.DefaultSystemOverlaySize), "system overlay size")
@@ -949,7 +949,7 @@ func newVMCreateCommand() *cobra.Command {
 		},
 	}
 	cmd.Flags().StringVar(&name, "name", "", "vm name")
-	cmd.Flags().StringVar(&imageName, "image", "", "image name or id")
+	cmd.Flags().StringVar(&imageName, "image", "", "image name or id (defaults to config's default_image_name; auto-pulled from imagecat if missing)")
 	cmd.Flags().IntVar(&vcpu, "vcpu", model.DefaultVCPUCount, "vcpu count")
 	cmd.Flags().IntVar(&memory, "memory", model.DefaultMemoryMiB, "memory in MiB")
 	cmd.Flags().StringVar(&systemOverlaySize, "system-overlay-size", model.FormatSizeBytes(model.DefaultSystemOverlaySize), "system overlay size")

internal/config/config.go

@@ -46,7 +46,7 @@ func Load(layout paths.Layout) (model.DaemonConfig, error) {
 		CIDR:                model.DefaultCIDR,
 		TapPoolSize:         4,
 		DefaultDNS:          model.DefaultDNS,
-		DefaultImageName:    "default",
+		DefaultImageName:    "debian-bookworm",
 	}
 
 	var file fileConfig

internal/config/config_test.go

@@ -35,8 +35,8 @@ func TestLoadDefaultsResolveFirecrackerAndGenerateSSHKey(t *testing.T) {
 			t.Fatalf("stat %s: %v", path, err)
 		}
 	}
-	if cfg.DefaultImageName != "default" {
-		t.Fatalf("DefaultImageName = %q, want default", cfg.DefaultImageName)
+	if cfg.DefaultImageName != "debian-bookworm" {
+		t.Fatalf("DefaultImageName = %q, want debian-bookworm", cfg.DefaultImageName)
 	}
 	if cfg.WebListenAddr != "127.0.0.1:7777" {
 		t.Fatalf("WebListenAddr = %q", cfg.WebListenAddr)

internal/daemon/autopull_test.go

@@ -0,0 +1,136 @@
+package daemon
+
+import (
+	"context"
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"banger/internal/imagecat"
+	"banger/internal/model"
+	"banger/internal/paths"
+	"banger/internal/system"
+)
+
+func TestFindOrAutoPullImageReturnsLocalWithoutPulling(t *testing.T) {
+	d := &Daemon{
+		layout: paths.Layout{ImagesDir: t.TempDir()},
+		store:  openDaemonStore(t),
+		runner: system.NewRunner(),
+		bundleFetch: func(context.Context, string, imagecat.CatEntry) (imagecat.Manifest, error) {
+			t.Fatal("bundleFetch should not be called when image is local")
+			return imagecat.Manifest{}, nil
+		},
+	}
+	id, _ := model.NewID()
+	if err := d.store.UpsertImage(context.Background(), model.Image{
+		ID:        id,
+		Name:      "my-local-image",
+		CreatedAt: model.Now(),
+		UpdatedAt: model.Now(),
+	}); err != nil {
+		t.Fatal(err)
+	}
+	image, err := d.findOrAutoPullImage(context.Background(), "my-local-image")
+	if err != nil {
+		t.Fatalf("findOrAutoPullImage: %v", err)
+	}
+	if image.Name != "my-local-image" {
+		t.Fatalf("Name = %q, want my-local-image", image.Name)
+	}
+}
+
+func TestFindOrAutoPullImagePullsFromCatalog(t *testing.T) {
+	imagesDir := t.TempDir()
+	kernelsDir := t.TempDir()
+	seedKernel(t, kernelsDir, "generic-6.12")
+
+	pullCalls := 0
+	d := &Daemon{
+		layout: paths.Layout{ImagesDir: imagesDir, KernelsDir: kernelsDir},
+		store:  openDaemonStore(t),
+		runner: system.NewRunner(),
+		bundleFetch: func(ctx context.Context, destDir string, entry imagecat.CatEntry) (imagecat.Manifest, error) {
+			pullCalls++
+			return stubBundleFetch(imagecat.Manifest{KernelRef: "generic-6.12"})(ctx, destDir, entry)
+		},
+	}
+	// "debian-bookworm" is in the embedded imagecat catalog.
+	image, err := d.findOrAutoPullImage(context.Background(), "debian-bookworm")
+	if err != nil {
+		t.Fatalf("findOrAutoPullImage: %v", err)
+	}
+	if image.Name != "debian-bookworm" {
+		t.Fatalf("Name = %q, want debian-bookworm", image.Name)
+	}
+	if pullCalls != 1 {
+		t.Fatalf("bundleFetch calls = %d, want 1", pullCalls)
+	}
+}
+
+func TestFindOrAutoPullImageReturnsOriginalErrorWhenNotInCatalog(t *testing.T) {
+	d := &Daemon{
+		layout: paths.Layout{ImagesDir: t.TempDir()},
+		store:  openDaemonStore(t),
+		runner: system.NewRunner(),
+	}
+	_, err := d.findOrAutoPullImage(context.Background(), "not-in-catalog-or-store")
+	if err == nil || !strings.Contains(err.Error(), "not found") {
+		t.Fatalf("err = %v, want not-found", err)
+	}
+}
+
+func TestReadOrAutoPullKernelReturnsLocalWithoutPulling(t *testing.T) {
+	kernelsDir := t.TempDir()
+	seedKernel(t, kernelsDir, "generic-6.12")
+	d := &Daemon{layout: paths.Layout{KernelsDir: kernelsDir}}
+
+	entry, err := d.readOrAutoPullKernel(context.Background(), "generic-6.12")
+	if err != nil {
+		t.Fatalf("readOrAutoPullKernel: %v", err)
+	}
+	if entry.Name != "generic-6.12" {
+		t.Fatalf("Name = %q", entry.Name)
+	}
+}
+
+func TestReadOrAutoPullKernelErrorsWhenNotInCatalog(t *testing.T) {
+	d := &Daemon{layout: paths.Layout{KernelsDir: t.TempDir()}}
+	_, err := d.readOrAutoPullKernel(context.Background(), "nonexistent-kernel")
+	if err == nil || !strings.Contains(err.Error(), "not found") {
+		t.Fatalf("err = %v, want not-found", err)
+	}
+}
+
+// TestReadOrAutoPullKernelSurfacesNonNotExistError covers the path where
+// kernelcat.ReadLocal fails for a reason other than missing entry (e.g.
+// corrupt manifest); the autopull logic should NOT try to fetch in that
+// case since the entry clearly exists in some broken form.
+func TestReadOrAutoPullKernelSurfacesNonNotExistError(t *testing.T) {
+	kernelsDir := t.TempDir()
+	// Seed a manifest that doesn't match the entry's own Name field —
+	// kernelcat.ReadLocal returns an error, not os.ErrNotExist.
+	dir := filepath.Join(kernelsDir, "broken-kernel")
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "manifest.json"), []byte(`{"name":"different-name"}`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	d := &Daemon{layout: paths.Layout{KernelsDir: kernelsDir}}
+	_, err := d.readOrAutoPullKernel(context.Background(), "broken-kernel")
+	if err == nil {
+		t.Fatal("want error")
+	}
+	// Must not be wrapped in an "auto-pull" message — the corrupt-manifest
+	// failure should surface as the primary cause.
+	if strings.Contains(err.Error(), "not found in catalog") {
+		t.Fatalf("err = %v, should not claim 'not in catalog'", err)
+	}
+	// Sanity: ensure it's not os.ErrNotExist-compatible.
+	if errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("err = %v, should not be os.ErrNotExist", err)
+	}
+}

internal/daemon/images.go

@@ -179,7 +179,7 @@ func (d *Daemon) RegisterImage(ctx context.Context, params api.ImageRegisterPara
 			}
 		}
 	}
-	kernelPath, initrdPath, modulesDir, err := d.resolveKernelInputs(params.KernelRef, params.KernelPath, params.InitrdPath, params.ModulesDir)
+	kernelPath, initrdPath, modulesDir, err := d.resolveKernelInputs(ctx, params.KernelRef, params.KernelPath, params.InitrdPath, params.ModulesDir)
 	if err != nil {
 		return model.Image{}, err
 	}
@@ -374,7 +374,10 @@ func firstNonEmpty(values ...string) string {
 
 // resolveKernelInputs canonicalises user-supplied kernel info: either direct
 // paths or a kernel-catalog ref. Shared by RegisterImage and PullImage.
-func (d *Daemon) resolveKernelInputs(kernelRef, kernelPath, initrdPath, modulesDir string) (string, string, string, error) {
+// When kernelRef is given but not yet pulled locally, an auto-pull from the
+// embedded kernelcat catalog fires so the caller doesn't have to manage
+// kernel/image ordering by hand.
+func (d *Daemon) resolveKernelInputs(ctx context.Context, kernelRef, kernelPath, initrdPath, modulesDir string) (string, string, string, error) {
 	kernelRef = strings.TrimSpace(kernelRef)
 	kernelPath = strings.TrimSpace(kernelPath)
 	initrdPath = strings.TrimSpace(initrdPath)
@@ -384,12 +387,9 @@ func (d *Daemon) resolveKernelInputs(kernelRef, kernelPath, initrdPath, modulesD
 		if kernelPath != "" || initrdPath != "" || modulesDir != "" {
 			return "", "", "", fmt.Errorf("--kernel-ref is mutually exclusive with --kernel/--initrd/--modules")
 		}
-		entry, err := kernelcat.ReadLocal(d.layout.KernelsDir, kernelRef)
+		entry, err := d.readOrAutoPullKernel(ctx, kernelRef)
 		if err != nil {
-			if os.IsNotExist(err) {
-				return "", "", "", fmt.Errorf("kernel %q not found in catalog; run 'banger kernel list' to see available entries", kernelRef)
-			}
-			return "", "", "", fmt.Errorf("resolve kernel %q: %w", kernelRef, err)
+			return "", "", "", err
 		}
 		return entry.KernelPath, entry.InitrdPath, entry.ModulesDir, nil
 	}
@@ -399,3 +399,27 @@ func (d *Daemon) resolveKernelInputs(kernelRef, kernelPath, initrdPath, modulesD
 	}
 	return kernelPath, initrdPath, modulesDir, nil
 }
+
+// readOrAutoPullKernel tries the local kernelcat first; on miss, checks
+// the embedded catalog and auto-pulls the bundle.
+func (d *Daemon) readOrAutoPullKernel(ctx context.Context, kernelRef string) (kernelcat.Entry, error) {
+	entry, err := kernelcat.ReadLocal(d.layout.KernelsDir, kernelRef)
+	if err == nil {
+		return entry, nil
+	}
+	if !os.IsNotExist(err) {
+		return kernelcat.Entry{}, fmt.Errorf("resolve kernel %q: %w", kernelRef, err)
+	}
+	catalog, loadErr := kernelcat.LoadEmbedded()
+	if loadErr != nil {
+		return kernelcat.Entry{}, fmt.Errorf("kernel %q not found locally: %w", kernelRef, loadErr)
+	}
+	if _, lookupErr := catalog.Lookup(kernelRef); lookupErr != nil {
+		return kernelcat.Entry{}, fmt.Errorf("kernel %q not found in catalog; run 'banger kernel list --available' to browse", kernelRef)
+	}
+	vmCreateStage(ctx, "auto_pull_kernel", fmt.Sprintf("pulling kernel %s from catalog", kernelRef))
+	if _, pullErr := d.KernelPull(ctx, api.KernelPullParams{Name: kernelRef}); pullErr != nil {
+		return kernelcat.Entry{}, fmt.Errorf("auto-pull kernel %q: %w", kernelRef, pullErr)
+	}
+	return kernelcat.ReadLocal(d.layout.KernelsDir, kernelRef)
+}

internal/daemon/images_pull.go

@@ -75,7 +75,7 @@ func (d *Daemon) pullFromOCI(ctx context.Context, params api.ImagePullParams) (i
 		return model.Image{}, fmt.Errorf("image %q already exists (id=%s); pick a different --name or delete it first", imgName, existing.ID)
 	}
 
-	kernelPath, initrdPath, modulesDir, err := d.resolveKernelInputs(params.KernelRef, params.KernelPath, params.InitrdPath, params.ModulesDir)
+	kernelPath, initrdPath, modulesDir, err := d.resolveKernelInputs(ctx, params.KernelRef, params.KernelPath, params.InitrdPath, params.ModulesDir)
 	if err != nil {
 		return model.Image{}, err
 	}
@@ -181,7 +181,7 @@ func (d *Daemon) pullFromBundle(ctx context.Context, params api.ImagePullParams,
 	if kernelRef == "" && strings.TrimSpace(params.KernelPath) == "" {
 		kernelRef = strings.TrimSpace(entry.KernelRef)
 	}
-	kernelPath, initrdPath, modulesDir, err := d.resolveKernelInputs(kernelRef, params.KernelPath, params.InitrdPath, params.ModulesDir)
+	kernelPath, initrdPath, modulesDir, err := d.resolveKernelInputs(ctx, kernelRef, params.KernelPath, params.InitrdPath, params.ModulesDir)
 	if err != nil {
 		return model.Image{}, err
 	}

internal/daemon/vm_create.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 
 	"banger/internal/api"
+	"banger/internal/imagecat"
 	"banger/internal/model"
 	"banger/internal/vmdns"
 )
@@ -35,7 +36,7 @@ func (d *Daemon) CreateVM(ctx context.Context, params api.VMCreateParams) (vm mo
 		imageName = d.config.DefaultImageName
 	}
 	vmCreateStage(ctx, "resolve_image", "resolving image")
-	image, err := d.FindImage(ctx, imageName)
+	image, err := d.findOrAutoPullImage(ctx, imageName)
 	if err != nil {
 		return model.VMRecord{}, err
 	}
@@ -129,3 +130,29 @@ func (d *Daemon) CreateVM(ctx context.Context, params api.VMCreateParams) (vm mo
 	}
 	return d.startVMLocked(ctx, vm, image)
 }
+
+// findOrAutoPullImage tries the local image store first; if the name
+// isn't registered but matches an entry in the embedded imagecat
+// catalog, it auto-pulls the bundle so `vm create --image foo` (and
+// therefore `vm run`) works on a fresh host without the user having
+// to run `image pull` first.
+func (d *Daemon) findOrAutoPullImage(ctx context.Context, idOrName string) (model.Image, error) {
+	image, err := d.FindImage(ctx, idOrName)
+	if err == nil {
+		return image, nil
+	}
+	catalog, loadErr := imagecat.LoadEmbedded()
+	if loadErr != nil {
+		return model.Image{}, err
+	}
+	entry, lookupErr := catalog.Lookup(idOrName)
+	if lookupErr != nil {
+		// Not in the catalog either — surface the original not-found.
+		return model.Image{}, err
+	}
+	vmCreateStage(ctx, "auto_pull_image", fmt.Sprintf("pulling %s from image catalog", entry.Name))
+	if _, pullErr := d.PullImage(ctx, api.ImagePullParams{Ref: entry.Name}); pullErr != nil {
+		return model.Image{}, fmt.Errorf("auto-pull image %q: %w", entry.Name, pullErr)
+	}
+	return d.FindImage(ctx, idOrName)
+}