one thing id add to the 'traditional practices still matter' point: in agentic systems with real side effects (API calls, sending messages, writing to external services), idempotency goes from nice to have to the primary reliability invariant.

in regular software, if a function runs twice you get a wrong answer. in an agent that sends outreach messages, a restart means every action replays. test coverage of the agent's logic won't catch this -- you have to explicitly design the execution graph so each node is restart-safe.

it's not a new problem -- distributed systems have dealt with exactly-once delivery forever. but agentic systems drag that infrastructure concern into application code in a way most teams aren't used to.