Validation is not static.

Testing a system at build time is necessary, but it is not sufficient. Real-world inputs are dynamic and unpredictable.

Runtime validation acts as a continuous quality gate. It verifies that inputs are safe and that outputs meet performance agreements.

When validation is static, it misses the changing context of production. Moving tests to the runtime path turns testing into active observability.

What this changes in practice: implement assertion-style checks directly in the production API path to flag anomalous outputs in real time.