Wake an idle agent when a teammate message arrives

The problem

agents_send delivers a message to a teammate, but the recipient does not act on it. The message is persisted and a notice appears in the recipient's terminal — then nothing happens until a human types something into that agent's pane.

Observed repeatedly: a coder finishes a ticket, messages the Code Reviewer, and the reviewer never starts. Pablo has to open the reviewer's tab and prompt it manually — either "read your inbox" or just re-issuing the original request by hand. The handoff step is therefore doing no work.

Why it happens (two causes, both real)

1. Agent sessions are turn-based. An idle agent is not running. Message arrival is a notification, not a turn trigger, so nothing executes until the next user turn.
2. The etiquette instructs agents to defer. roles/_etiquette.md says, verbatim: "Finish the task in front of you first; the message is durable and waits" and "Dropping your user's question to go and service an inbox is the one reaction that is always wrong." That is correct for a BUSY agent and wrong for an IDLE one, but the text does not distinguish the two.

Requested behaviour

When a message arrives for an agent that is idle (no turn in flight), start a turn so it reads its inbox and acts — the way a scheduled task or a team run already starts an agent by itself.

Cause 2 needs a matching edit: the etiquette should say "finish the task in front of you first" only when there IS a task in front of you. An idle agent receiving work should take it.

Checked and ruled out

All 120 settings were listed (settings_list). There is no auto-wake, inbox-polling, or message-triggered-start option. autoLaunchAgentsAtStartup covers app launch, not incoming mail. So this is a missing capability, not a misconfiguration.

Problem to solve

Not hard, just tedious to say "check your messages" or basically just retype what the other agent already typed.

Proposed behavior

Automatically.

Who benefits

I'm guessing a lot of people, specially the full vibe-coders with workflows in place.

Acceptance criteria

Agent A requests an action from Agent B. Having both agents open, Agent B is IDLE and then starts doing (automatically) what Agent A asked for.