DeltaSnap skill for AI agents

An Agent Skill that teaches coding agents to take APFS safety checkpoints with DeltaSnap before making risky file changes, verify the blast radius with a diff, and recover individual files when a change goes wrong.

Snapshots are copy-on-write, so a checkpoint takes milliseconds and copies no data. The skill uses --safety snapshots, which expire on their own, so an abandoned agent session cannot pile up permanent snapshots.

Requires macOS with the DeltaSnap helper installed and its dsnap CLI on the machine. The skill stops and tells you if dsnap is missing rather than silently working without checkpoints.

Install

Claude Code

/plugin marketplace add scaleninja/deltasnap
/plugin install deltasnap@scaleninja
/reload-plugins

The skill is model-invoked: Claude loads it on its own when a task involves risky or bulk file changes. You can also invoke it directly with /deltasnap:deltasnap.

To install it without the plugin system, copy skills/deltasnap/ to ~/.claude/skills/deltasnap/ (all projects) or .claude/skills/deltasnap/ (one project).

Codex

Add this repo to ~/.agents/plugins/marketplace.json:

{
  "name": "scaleninja",
  "plugins": [
    {
      "name": "deltasnap",
      "source": { "source": "github", "repo": "scaleninja/deltasnap" },
      "policy": { "installation": "AVAILABLE", "authentication": "NONE" },
      "category": "Productivity"
    }
  ]
}

Then restart Codex and install DeltaSnap from the Plugins Directory. To install it by hand instead, copy skills/deltasnap/ to ~/.agents/skills/deltasnap/ or .codex/skills/deltasnap/.

Other agents

The skill is a plain SKILL.md. Copy skills/deltasnap/ into whatever skills directory your agent reads, or paste the body of the file into AGENTS.md or your system prompt.

Layout

.claude-plugin/
  marketplace.json   Claude Code marketplace catalog
  plugin.json        Claude Code plugin manifest
.codex-plugin/
  plugin.json        Codex plugin manifest
skills/
  deltasnap/
    SKILL.md         the skill itself, shared by both

Both ecosystems read the same skills/ directory, so there is one copy of the skill to maintain.

What the skill does

• Checkpoints the volume before a change round and tags the snapshot with machine-readable session metadata.
• Checkpoints again after the round and diffs the two, so unexpected paths surface before they compound.
• Recovers files by mounting the earlier checkpoint read-only and copying out of it. It never rolls back a whole volume.
• Refuses to delete snapshots it did not create, and never uses destroy --all-snapshots or --force.

Snapshots share the disk with your live data. They protect against agent mistakes, not against disk loss. They are not a backup.