Mirrors vs hand-written mocks
Mocks are written by people and go stale; a mirror is rebuilt from the traces the agent keeps producing.
Where they differ
Mocks encode what a developer remembered; a mirror encodes what the backend did.
A mirror reports drift per tool when the backend changes.
When to pick which
hand-written mocks remains the right tool when its own strengths are what you need; a mirror is for testing an agent against a backend that behaves like production without being production.
Related: /glossary/mirror/pricing