When a tool call times out, did it happen?

The idea in brief

When an agent's tool call times out, the action may have succeeded without the response arriving. A blind retry could create a second ticket or repeat a payment. This is a long-standing distributed-systems problem, and the established answers apply to agents too.

Idempotency keys

AWS's Builders' Library article "Making retries safe with idempotent APIs" (2021) describes the approach used across many AWS APIs:

• The caller sends a unique client request identifier, such as ClientToken in EC2, and reuses it on every retry.
• The service records that identifier atomically with the change it makes.
• A retry with the same identifier gets a response equivalent to the original, instead of a second action.
• Reusing an identifier with different parameters is rejected as a validation error.

For agents, the identifier needs to be created by the workflow before the tool call, not by the model, so a retry carries the same key.

Durable execution

In The AI Kubernetes Show episode on durable execution, Mark Fussell, creator of Dapr, describes runtimes that save state at each step so a crashed process can resume from its last completed step. He suggests keeping workflows deterministic where possible and using the model only for the decisions that need it.

Check before retrying

Emerson Braun's Conf42 Observability 2026 talk makes a related point: treat failures as states, classify them (a timeout is not the same as an invalid result), verify what actually happened, and only then retry, reroute, compensate or escalate. The talk's demo used a status check after a timeout to confirm that a refund had already gone through.

Matching autonomy to risk

The same talk suggests bounding how much an agent may do on its own by the risk of the action:

@article{adam2026toolcalltimeouts,
  title   = {When a tool call times out, did it happen?},
  author  = {Adam, Ammar},
  journal = {www.ammaradam.dev},
  year    = {2026},
  month   = {Sep},
  url     = {https://www.ammaradam.dev/posts/tool-call-timeouts/}
}