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The execution boundary

When you run nanny run, Nanny becomes the parent process of your agent. It reads [start].cmd from nanny.toml, spawns it as a child, and owns the process lifecycle — it decides when the process lives and when it dies. The moment any limit is crossed, Nanny kills the child process immediately — the process cannot catch, delay, or prevent the stop. An ExecutionStopped event is emitted with the reason, and Nanny exits with a non-zero status code.

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Multi-agent governance

When multiple agents run in the same process — as in CrewAI, LangGraph, AutoGen, or any framework that orchestrates agents within a single Python or Rust runtime — the enforcement model above applies to all of them simultaneously. A single nanny run governs the entire fleet. Each agent activates its own named limit set via @agent("role"). Tool calls from any agent flow through the same enforcement bridge. Each agent’s budget is tracked independently — hitting the analysis budget does not kill the reporter. Scope: All agents in the diagram run within one process. This covers any framework that orchestrates agents in a single runtime. Cross-process and cross-machine fleet enforcement is the v0.2.0 cloud layer.

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What Nanny enforces

All three limits are enforced on every run:
LimitRequirementBehaviour
timeoutNone — works for any processKilled when wall-clock time exceeds the configured value
stepsRust SDK or Python SDKKilled when step count reaches the configured limit
costRust SDK or Python SDKKilled when accumulated cost reaches the configured budget
Timeout enforcement works for any process in any language — no SDK required. Step and cost enforcement require the agent to report tool calls — either via the Rust SDK macros or the Python SDK decorators.

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Passthrough mode

When running outside nanny run, every macro becomes a no-op: 
#[tool(cost = 10)]
fn search(query: &str) -> String {
    // runs normally, no enforcement
}
This means you can ship instrumented code and run it in development, CI, and production without Nanny — until you explicitly wrap it with nanny run. The behaviour is identical either way.