[P0] arbitrum-cli: add 'cr8' subcommand group (agent-first MCP surface)

[abhicris]

Goal

Make kcolbchain/arbitrum-cli the official agent-first CLI for Create Protocol by adding a cr8 subcommand group. LLM-driven agents call these via MCP tool-use; humans get the same verbs via shell. JSON in, JSON out. This keeps Create Protocol operable by agents without requiring a custom-built SDK install.

Subcommands to spec

• arbitrum-cli cr8 register --profile <json> — calls AgentDeposit.register, emits agent id.
• arbitrum-cli cr8 deposit --amount <usdc> / withdraw.
• arbitrum-cli cr8 tasks list --agent <id> --status <open|claimed|done>.
• arbitrum-cli cr8 claim <task_id> / complete <task_id> --receipt <json>.
• arbitrum-cli cr8 balance --agent <id> — USDC + syUSD breakdown.
• arbitrum-cli cr8 watch --agent <id> — streams registry events as newline-delimited JSON.

All commands must pass the MCP-compatibility gate (structured error object, idempotent where possible, no interactive prompts).

Success criterion

• Spec specs/arbitrum-cli-cr8-subcommand.md merged here with the full verb table and JSON schemas.
• Tracking issue opened on kcolbchain/arbitrum-cli linking back here.
• One worked example in the spec showing an LLM agent completing a task purely via CLI tool calls.

Related

• kcolbchain/arbitrum-cli
• kcolbchain/arka — SDK shares the same verbs

— kcolbchain / Abhishek Krishna