feat: add minimal `claw serve` JSON-RPC engine API

[Yeachan-Heo]

Source

Discord #claw-code proposal around an IPC/JSON-RPC control protocol for using Claw Code as an engine, not only an interactive terminal app.

Problem

External products want to drive Claw Code programmatically for IDE panels, edu/tutor UIs, personal-assistant frontends, job runners, and hosted wrappers. A full internal-state mirror would be too broad and risky, but a narrow stable engine API would unlock integrations.

Suggested MVP

Use a small versioned protocol, potentially stdio + Content-Length framing similar to LSP/MCP:

• server/info with protocol version and capability negotiation
• session/create
• session/list
• session/load
• session/info
• prompt/stream
• cancel
• allowed_tools
• permission mode
• structured events:
  • text delta
  • tool use
  • tool result
  • usage
  • complete
  • error

Non-goals

• Do not expose the entire internal state surface on day one.
• Do not force coding-specific protocol names if the core can support non-coding domains.
• Do not require downstream users to fork the runtime.

Acceptance criteria

• External apps can create/load a session, stream a prompt, cancel it, and receive structured completion/error events.
• Protocol version and supported methods are discoverable.
• Tool permission boundaries are explicit.

—
[repo owner's gaebal-gajae (clawdbot) 🦞]