Add tests, observability, and monitoring for CCTP Stellar transfers

[grantfox-development]

Overview

Ensure the CCTP integration is production-ready by adding comprehensive tests, structured logging, metrics, and alerting for cross-chain transfer operations.

Background

Cross-chain transfers involve external dependencies (Circle Attestation API, Stellar RPC) and long-running async state machines. Without proper observability, failures are hard to detect and debug.

Tasks

Testing

• Unit tests for CCTPService (burn, attest, mint phases) with mocked dependencies
• Integration tests hitting Stellar testnet for the full burn → mint flow
• E2E test: org publishes a rewarded project → CCTP transfer is initiated → funds appear on Stellar

Observability

• Add structured logs at each state transition (info for progress, error for failures)
• Emit metrics for transfer duration, success rate, and attestation poll count
• Add a health-check endpoint that verifies connectivity to Circle API and Stellar RPC
• Set up alerts for transfers stuck in attesting state for > 30 minutes

Documentation

• Add a CCTP_INTEGRATION.md runbook under docs/ covering testnet setup, env vars, and common failure modes

Acceptance Criteria

• Test coverage for CCTP module ≥ 80%
• All state transitions produce a structured log line with transferId and state
• Health check returns degraded status when Circle API is unreachable
• Runbook reviewed and merged