orchestration: add typed agent-to-agent messaging over local IPC

[guicybercode]

Context

Agent communication must not be implemented by simulating keyboard input in another terminal. It needs a typed local protocol that works across vendors and preserves task/session identity.

Goal

Provide an agent-facing local command and daemon message bus for listing peers, sending messages, acknowledging delivery, waiting for replies, and reading status.

A possible CLI surface is agentctl or a cli-master agent subcommand; the final name should follow an ADR.

Scope

• Define sender, recipient, task, session generation, message ID, correlation ID, and bounded payload types.
• Route only between registered task assignments and live/reconnectable sessions.
• Add idempotent delivery and explicit acknowledgement/result states.
• Expose a minimal skill/instruction document for supported agent CLIs.
• Persist metadata required for audit/recovery without persisting secrets or raw terminal output.
• Add per-task queue limits, rate limits, and cancellation.

Acceptance criteria

• No operation writes directly into another terminal's keyboard stream without adapter-mediated delivery.
• A stale session generation cannot receive a message intended for its replacement.
• Duplicate message IDs do not execute twice.
• Slow or disconnected recipients cannot block PTY readers or daemon clients.
• Queue overflow is explicit and recoverable.
• Users can inspect sender, recipient, state, and timestamps.
• Unknown recipients and cross-task sends fail closed.
• Tests cover reconnect, duplicate delivery, timeout, cancellation, and concurrent sends.

Out of scope

Remote networking, cross-machine agents, and arbitrary peer-to-peer sockets.