The anatomy of a production-grade agent loop: retries, timeouts, checkpointing, and why most frameworks get this wrong.
What most agent loops get wrong
The standard ReAct loop is elegant on paper: reason, act, observe, repeat. In practice, production agent loops need to handle a much longer list of failure modes: LLM timeouts, tool errors, context length limits, rate limits, and mid-loop process crashes.
Most frameworks handle none of these gracefully. They raise an exception and stop. The loop is gone. You start again.
The layers of resilience
A production-grade agent loop needs at least three layers:
Layer 1: Tool-level retries. Individual tool calls should retry on transient errors (network timeouts, 429 rate limits) with exponential backoff. The agent loop should not see these retries — they're invisible to the reasoning layer.
Layer 2: Checkpointed state. After every successful tool call, the state is persisted. If the process crashes, the loop can resume from the last checkpoint without re-executing completed steps. (See our post on crash recovery for how this works in AgentState.)
Layer 3: Loop-level timeouts and step limits. Every agent run should have a wall-clock timeout and a maximum step count. Without these, a confused agent can run indefinitely, burning compute and API budget.
The SDK handles this for you
The TomorrowCentral SDK implements all three layers by default. You pass a goal, optionally set max_steps and timeout, and the loop handles the rest. Tool retries are configurable per-tool. State is checkpointed automatically after each step.
What you get is an agent loop that degrades gracefully — a crash becomes a resume, a timeout becomes a clean exit with the last known state preserved.
Designing for resumability
The most important architectural insight is this: design your tools to be idempotent. If a tool might be called again on resume, it should either check whether its work is already done (e.g., check if the file already exists before writing) or be naturally safe to call twice (e.g., a read-only data fetch).
With idempotent tools and a checkpointed loop, your agents are safe to resume from any point.