-- Phase 2.2: add trace_id to token_usage_logs for cost attribution (idempotent)
SET @db = DATABASE();
SET @col_exists = (SELECT COUNT(*) FROM information_schema.columns WHERE table_schema = @db AND table_name = 'token_usage_logs' AND column_name = 'trace_id');
SET @sql = IF(@col_exists = 0, 'ALTER TABLE token_usage_logs ADD COLUMN trace_id VARCHAR(64) NULL DEFAULT NULL', 'SELECT 1');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;