await sdk.transport.message.send({
  to:         'alice.gao',       // recipient's Gao Domain or routing tag
  content:    'Hello!',
  type?:      'text',            // 'text' | 'notification' | 'agent_action'
  encrypted?: true,              // default true — always E2EE
})

const unsub = sdk.transport.message.subscribe((msg: IncomingMessage) => {
  console.log(msg.from)                // sender's domain
  console.log(msg.decrypted.content)  // decrypted message text
  console.log(msg.decrypted.type)     // message type
  console.log(msg.timestamp)          // unix ms
})

// Stop listening (call on component unmount)
unsub()

---

### Agent Sends as Bot Identity

When an agent sends a message, it appears as the agent’s identity — not the domain owner.

await sdk.transport.message.sendAsAgent(
  'booking-bot-id',         // agent ID registered in sdk.intelligence
  'customer-routing-tag',   // recipient
  'Your appointment is confirmed for tomorrow at 3pm.'
)

// Select best relay node for routing
const route = await sdk.transport.selectRoute({
  recipient: 'alice.gao',
  priority: 'low_latency',    // 'low_latency' | 'high_reliability'
})

// Validate a relay path
const valid = await sdk.transport.validateRelayPath(['relay1.meshii.app', 'relay2.meshii.app'])

---

### React Hook

import { useMessages } from '@gao/system-sdk/react'

function ChatWindow({ contact }: { contact: string }) {
  const { messages, send, loading } = useMessages(sdk, contact)

  return (
    <div>
      {messages.map(msg => (
        <div key={msg.id} className={msg.from === sdk.domain ? 'sent' : 'received'}>
          {msg.decrypted.content}
        </div>
      ))}
      <input
        onKeyDown={(e) => {
          if (e.key === 'Enter') send(e.currentTarget.value)
        }}
      />
    </div>
  )
}

// Default — no storage
sdk.transport.setStorageMode('none')

// Save locally on device (encrypted)
sdk.transport.setStorageMode('local')

// Backup to GaoStorage (encrypted, user pays fee)
sdk.transport.setStorageMode('depin')

---

### Privacy Model

What relay sees

What relay cannot see

Routing tag (opaque recipient ID)

Message content

Ciphertext blob

Sender identity (in plaintext)

TTL timestamp

Conversation history

Messages are deleted from relay **immediately on delivery ACK**. Maximum TTL is 7 days — after which undelivered messages are purged automatically.

---

### Common Patterns

#### Booking Confirmation

await sdk.transport.message.send({
  to: customerDomain,
  content: `✓ Confirmed: ${service} on ${date} at ${time}. Reply to reschedule.`,
  type: 'notification',
})

#### Payment Notification

await sdk.transport.message.send({
  to: merchantDomain,
  content: JSON.stringify({
    type: 'payment_received',
    amount: '25.00',
    currency: 'USDC',
    from: customerDomain,
  }),
  type: 'agent_action',
})

#### Support Bot

const unsub = sdk.transport.message.subscribe(async (msg) => {
  if (msg.decrypted.type === 'text') {
    const reply = await sdk.intelligence.runAgent('support-bot', msg.decrypted.content)
    await sdk.transport.message.sendAsAgent('support-bot', msg.from, reply.output)
  }
})