After enough agents, the failures stop looking like surprises and start looking like a short list. Four classes account for most of what we see, and each one is visible from the design, before any code runs.
1. The Retry Loop
An agent calls a tool, the call is flaky, and there is no timeout and no cap on retries. It spins. You can see this the moment a tool with real-world latency sits in the path without a guard around it.
2. Schema Drift
The agent writes to a record whose shape has moved since the plan was drawn. The write fails, or worse, half-succeeds. Any write target that is not pinned by a contract is a candidate.
3. State Deadlock
Multi-turn memory locks up past some turn threshold. Long sessions stall. If the design holds conversation state without a bound, the deadlock is already there.
4. PII Leakage
Private data reaches the model prompt unredacted. The path from a data source to a model call, with no redaction step in between, is the whole tell.
None of these need a running agent to find. They need the goal, the data, and the tools laid out as paths. That is what a Faultmap does.