Fork the current Claude Code session into a fresh AgentBox box.

Resolve the provider flag from $ARGUMENTS:
- empty → no flag (uses the default docker provider)
- docker | daytona | hetzner | vercel | e2b → pass --provider $ARGUMENTS
- anything else → stop and tell the user the valid values are docker, daytona, hetzner, vercel, e2b
Detect an active plan (optional --plan). If this session was just working on a Claude Code plan, carry it into the box so the fork resumes in plan mode.
- If you know the plan file path for this session (plan mode writes it to ~/.claude/plans/<slug>.md, and you have it from the plan you just produced in this conversation), use that path.
- Otherwise, find the most recent plan only if it was touched in the last 15 minutes (a stale plan from another task should not be resurrected). Run via the Bash tool:
```
find "$HOME/.claude/plans" -name '*.md' -mmin -15 -type f 2>/dev/null \
  | xargs -r ls -t 2>/dev/null | head -1
```
  If it prints a path, that's the current plan; if it prints nothing, there is no active plan — skip --plan.

agentbox