feat: portable OCX home export/import for air-gapped environments

[michael-herwig]

Context

An OCX home directory already contains everything needed for offline package use: content-addressed objects, a local index with resolved metadata, and install symlinks. Packaging this into a self-contained archive would enable air-gapped deployments without a registry.

This depends on #23 (relative symlinks within OCX home) to ensure the archive is relocatable.

Ref: Nesbitt's article on OCI and package registries notes that .deb/.rpm files are self-contained while OCI artifacts require manifest + blobs. OCX's local store already bridges this gap — this feature formalizes it.

Proposed Commands

ocx export [packages...] --output <path.tar.gz>
ocx import <path.tar.gz> [--home <target>]

Export

• Resolves the specified packages (or all installed) to their object store entries + index data
• Creates a tar archive containing the subset of OCX home needed for those packages
• Symlinks within the archive are relative (depends on relative symlinks feature)
• Index entries included so ocx commands work offline against the imported home

Import

• Extracts into target $OCX_HOME (or a specified path)
• Merges with existing content (content-addressed = no conflicts for identical digests)
• Recreates install symlinks

Relationship to OCI Layout

OCI defines an image layout format for on-disk storage. We should evaluate whether export should produce:

1. An OCX-native archive (simpler, works with ocx import only)
2. An OCI layout directory (interoperable with oras, skopeo, crane)
3. Both (OCX-native as default, --format oci-layout option)

Depends On

• feat: relative symlinks within OCX home for relocatable stores #23 — Relative symlinks within OCX home