Bulletproofing LLM Structured Output in Python: Healing Retries, Cost Caps, and Drift Detection (Runnable Code)

Short summary

JSON mode catches syntax errors but misses real production failures: refusals, semantic drift, type coercion, and silent truncation. This guide presents a four-layer solution—strict validation beyond JSON mode, healing retry loops, cost-bounded fallbacks, and drift detection—with complete production-ready Python code ready to drop into FastAPI. Based on two months of incident logs from enterprise deployments.

• •JSON mode alone fails on refusals, semantic drift, type coercion, and truncation in production
• •Four-layer solution: strict validation, healing retry loop, cost caps, drift detection
• •Complete runnable Python code with Pydantic schemas and FastAPI integration

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