BACKEND: Contest Join Flow with PrizePool Integration

Description
Handle contest entry by interacting with StarkNet's PrizePool contract.

Acceptance Criteria

• POST /contests/:id/join
  1. Verify JWT and contest exists
  2. Call PrizePool.lock_funds(entryFee) via StarkNet.js
  3. Store transaction hash in participations table
  4. Increment contest participant count
• Handles transaction errors (e.g., insufficient funds)
• Returns { txHash: string } on success

Technical Details

const contract = new Contract(PrizePoolABI, PRIZE_POOL_ADDRESS, provider);
const { transaction_hash } = await contract.lock_funds(
  userAddress,
  entryFee
);

Notes

• Use StarkNet.js v5.0+
• Implement transaction status polling (ACCEPTED_ON_L2)

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