[Lower priority] Multi-device orchestration (coordinated actions across two devices)

**Priority:** Lower / backlog.

Support coordinated actions across two devices (e.g. two simulators or two emulators): messaging between them, share flows, Handoff-like behavior. This would enable E2E scenarios that involve two devices (e.g. "send from device A, receive on device B"). Design would need to address session model (two sessions? one session with two devices?) and CLI/API shape.

**Acceptance criteria (high level):**
- [ ] Define session/CLI model for two devices
- [ ] At least one scenario: trigger action on device A, verify result on device B (e.g. share or message)