[PHASE 3] Add Structured Logging & Observability #608

class Logger {
  constructor(level = 'info') {
    this.level = level;
    this.levelMap = { debug: 0, info: 1, warn: 2, error: 3 };
  }
  
  log(level, message, data = {}) {
    if (this.levelMap[level] >= this.levelMap[this.level]) {
      const output = {
        timestamp: new Date().toISOString(),
        level,
        message,
        ...data
      };
      const stream = level === 'error' ? stderr : stdout;
      stream.write(JSON.stringify(output) + '\\n');
    }
  }
  
  debug(message, data) { this.log('debug', message, data); }
  info(message, data) { this.log('info', message, data); }
  warn(message, data) { this.log('warn', message, data); }
  error(message, data) { this.log('error', message, data); }
}

module.exports = { Logger };

const { Logger } = require('../utils/logger');
const logger = new Logger(process.env.LOG_LEVEL || 'info');

async function run(context) {
  const startTime = Date.now();
  logger.info('Agent started', { event: 'start' });
  
  try {
    // ...
    logger.info('Agent finished', {
      event: 'complete',
      duration: Date.now() - startTime,
      itemsProcessed: 5
    });
  } catch (error) {
    logger.error('Agent failed', {
      event: 'error',
      error: error.message,
      duration: Date.now() - startTime
    });
  }
}