Phase 2: daemon PullImage orchestration

(d *Daemon).PullImage downloads an OCI image, flattens it into an
ext4 rootfs, and registers the result as a managed banger image.

Flow (internal/daemon/images_pull.go):
 1. Parse + validate the OCI ref via go-containerregistry/name.
 2. Derive a friendly default name from the ref ("debian-bookworm")
    when --name is omitted.
 3. Reject if an image with that name already exists.
 4. Resolve kernel info via the new shared resolveKernelInputs
    helper (refactored out of RegisterImage); ValidateKernelPaths
    checks the kernel triple alone.
 5. Acquire imageOpsMu, generate a fresh image id, and stage at
    <ImagesDir>/<id>.staging.
 6. imagepull.Pull → cache layers under OCICacheDir;
    imagepull.Flatten → temp rootfs tree under os.TempDir (so the
    state filesystem doesn't temporarily double in size).
 7. Default size: max(treeSize × 1.25, 1 GiB); --size override
    accepted.
 8. imagepull.BuildExt4 produces the rootfs.ext4 in the staging dir.
 9. imagemgr.StageBootArtifacts stages the kernel/initrd/modules
    into the same dir (reused unchanged).
 10. Atomic os.Rename(staging, finalDir) publishes the artifact dir.
 11. Persist model.Image with Managed=true. Failure at any step
     removes the staging dir; failure post-rename removes finalDir.

The pullAndFlatten field on Daemon is the test seam: tests stub it
to write a fixture tree into destDir and skip the real registry.

Refactor: extracted the "kernel-ref vs direct paths" resolution
out of RegisterImage into d.resolveKernelInputs so PullImage and
RegisterImage share one source of truth for that policy. Split
ValidateRegisterPaths into a kernel-only ValidateKernelPaths so
PullImage (which produces the rootfs itself) can validate just
the kernel triple without the rootfs check.

API: ImagePullParams { Ref, Name, KernelPath, InitrdPath,
ModulesDir, KernelRef, SizeBytes }. RPC dispatch case image.pull
mirrors image.register.

Tests cover: happy-path producing a managed image with all four
artifacts present + staging cleaned up, name-collision rejection,
missing-kernel rejection, and staging cleanup on a failed pull.
defaultImageNameFromRef handles tag/digest/no-suffix cases.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/daemon/imagemgr/paths.go

@@ -21,17 +21,29 @@ import (
 func ValidateRegisterPaths(rootfsPath, workSeedPath, kernelPath, initrdPath, modulesDir string) error {
 	checks := system.NewPreflight()
 	checks.RequireFile(rootfsPath, "rootfs image", `pass --rootfs <path>`)
-	checks.RequireFile(kernelPath, "kernel image", `pass --kernel <path>`)
 	if workSeedPath != "" {
 		checks.RequireFile(workSeedPath, "work-seed image", `pass --work-seed <path> or rebuild the image with a work seed`)
 	}
+	addKernelChecks(checks, kernelPath, initrdPath, modulesDir)
+	return checks.Err("image register failed")
+}
+
+// ValidateKernelPaths checks the kernel triple alone, used by flows
+// (e.g. image pull) that produce the rootfs themselves.
+func ValidateKernelPaths(kernelPath, initrdPath, modulesDir string) error {
+	checks := system.NewPreflight()
+	addKernelChecks(checks, kernelPath, initrdPath, modulesDir)
+	return checks.Err("kernel preflight failed")
+}
+
+func addKernelChecks(checks *system.Preflight, kernelPath, initrdPath, modulesDir string) {
+	checks.RequireFile(kernelPath, "kernel image", `pass --kernel <path>`)
 	if initrdPath != "" {
 		checks.RequireFile(initrdPath, "initrd image", `pass --initrd <path>`)
 	}
 	if modulesDir != "" {
 		checks.RequireDir(modulesDir, "kernel modules dir", `pass --modules <dir>`)
 	}
-	return checks.Err("image register failed")
 }
 
 // ValidatePromotePaths checks that an existing registered image's artifacts