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Overview

Many “agents” are just controlled loops:
  • Run an iteration body
  • Decide whether to stop
  • Enforce budgets/timeouts
  • Optionally checkpoint or interrupt
In Coevolved, this pattern is packaged as agent_loop(...), which returns a Step you can compose like any other step.

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LoopPolicy and LoopState

LoopPolicy controls loop execution:
  • max_iterations
  • timeout_seconds
  • Optional checkpoint_store + checkpoint_policy
  • Optional execution_policy (budgets)
LoopState tracks iteration index, elapsed time, and the last checkpoint id.

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Checkpointing and budgets in loops

The loop can checkpoint before/after each iteration and on errors/interrupts. If a usage policy is configured, the loop checks budget before each iteration.

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Stop conditions

The stop condition is a function: (state) -> bool. Keep it:
  • Explicit (no hidden globals)
  • Cheap (evaluated every iteration)
  • Testable (unit tests should cover stop behavior)

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Next steps

ReAct agent

A concrete agent loop pattern: plan with LLM, act with tools.

prebuilt.loop reference

agent_loop, LoopPolicy, and LoopState API details.