Implement Trade Execution Service

[Mathews-25]

Context:
When users swipe right, the backend must execute trades automatically via Soroban contracts with risk controls (position limits, stop-loss).

Problem:
Build a trade execution service that validates trades, invokes Soroban contracts, and tracks execution status.

What Done Looks Like:

• POST /trades/execute endpoint
• Trade validation against risk limits
• Soroban contract invocation
• Transaction status tracking
• Success/failure notifications

Folder Structure:

src/
├── trades/
│   ├── trades.service.ts
│   ├── trades.controller.ts
│   ├── trades.module.ts
│   ├── entities/
│   │   └── trade.entity.ts
│   ├── services/
│   │   ├── trade-executor.service.ts
│   │   └── risk-manager.service.ts
│   └── dto/
│       ├── execute-trade.dto.ts
│       └── trade-result.dto.ts

Implementation Guidelines:

• Validate user has sufficient balance
• Check position limits (max 10 open positions per user)
• Verify signal still active and not expired
• Invoke Soroban trade executor contract
• Store trade record in database
• Track transaction hash and status
• Emit event for notifications
• Target <5s execution time

Trade Validation:

1. User authenticated
2. Signal exists and active
3. Sufficient balance for trade + fees
4. Within position limits
5. Risk parameters valid

Trade Entity Fields:

• id, user_id, signal_id, status
• entry_price, amount, side (BUY/SELL)
• tx_hash, executed_at
• pnl, closed_at

Edge Cases:

• Insufficient balance mid-execution
• Signal expired during execution
• Network congestion causing timeout
• Duplicate trade prevention

Validation:

• Valid trade executes successfully
• Invalid trade rejected with clear error
• Transaction hash stored
• Status updates correctly