CLI command to send messages to inactive sessions (pending queue)

[lucharo]

Summary

The phone app can send messages to inactive sessions — they get queued server-side and delivered when the session reconnects (pendingCount increments). The CLI has no equivalent. happier session run stream-start only works for active sessions (connected via socket.io) and fails with "RPC method not available" for inactive ones.

Use Case

Building a TUI session manager that lists all relay sessions and lets you message any of them. Currently:

• Active session → stream-start/stream-read works
• Inactive session → no way to send a message from the CLI

The phone app handles this seamlessly — you can type a message to any session regardless of whether it's active. The message sits in the relay's pending queue until the session reconnects.

Proposed Solution

happier session send <session-id> <message> [--json]

This would use the same relay server-side pending queue mechanism that the phone app uses. The message gets delivered when the session reconnects, or immediately if the session is active.

Response:

{
  "ok": true,
  "kind": "session_send",
  "data": {
    "sessionId": "cmm...",
    "delivered": false,
    "pendingCount": 3
  }
}

Where delivered: true means the session was active and received it immediately, delivered: false means it's queued.

Context

Related: #133 (expose continueWithReplay on HTTP API)

The relay already has the pending message infrastructure — the phone app uses it. This just needs a CLI surface.

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