Agents are tested as distributions
Traditional unit tests still matter for tools, parsers, schemas, and permission checks. But agent behavior is non-deterministic, so the system also needs dataset evals, trace grading, adversarial cases, and human correction metrics.
Security is mostly about boundaries
Prompt injection is not solved by another prompt. Treat external text as data, not authority. Separate trusted instructions from untrusted content. Put dangerous tools behind executor policy and human review. Redact secrets from traces but keep enough structure to debug.
Deploy by blast radius
A draft-writing agent can run synchronously with cheap rollback. A deployment agent needs background execution, approval interrupts, resumable state, cancellation, audit logs, and staged rollout. Same model family, different product boundary.