This is Part 2 of a three-part field manual on engineering production agentic systems. Part 1 took context engineering. This part takes guardrails. Part 3 takes human-in-the-loop topology. The conviction underneath all three: production agentic systems are won on these three architectural disciplines — not on model choice.
The Opening Claim
MCP gateways have made tool exposure cheap. Wrapping a hundred internal APIs as agent-callable tools is now a one-day job, sometimes a one-hour job. Tool correctness, though — making sure the agent picks the right tool, with the right parameters, under the right authorization, with the right human review — is not cheap. It is the work nobody talks about in agentic-AI demos, and it is where production systems either hold up or collapse.
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