Soft Constraints vs. Hard Constraints in LLM Systems: Why the Mismatch Causes Real Failures
Most LLM system failures don't come from the model being wrong. They come from the system being wrong about what the model can enforce. When you write "never reveal customer data" in a system prompt and treat that as equivalent to "revoke the database credential," you have introduced a category error that will eventually cause a security incident, a reliability failure, or a broken user experience — and you won't know which one until it happens in production.
The distinction between soft constraints and hard constraints is architectural, not stylistic. Getting it wrong doesn't produce style regressions. It produces breaches.
