Idempotency and recovery in agent tool calls

  **Idempotency and recovery in agent tool calls** is the practice of resuming or retrying an interrupted tool operation without silently duplicating its external effects or misreporting an uncertain outcome as success or failure. It combines an operation identity, the tool's documented retry contract, durable local state, reconciliation against the target system, and explicit [completion verification](/wiki/verifying-completion-in-tool-using-agents). This article is an engineering synthesis for digital tool calls; it is not a claim that idempotency keys provide universal exactly-once execution.    ## Why recovery is a separate problem    A tool-using agent can lose certainty at several boundaries: before a request is sent, after the service receives it but before the client receives a response, while an asynchronous job is running, or after the service completes an action but before the agent records the result. The same timeout can therefore describe materially different states. Retrying may be harmless, may create a duplicate payment or resource, or may return a stored result, depending on the operation and the service contract.    … 85 unchanged lines …    - [Idempotency keys](/wiki/idempotency-keys) covers server contracts, scope, retention, and provider comparisons.  - [Verifying completion in tool-using agents](/wiki/verifying-completion-in-tool-using-agents) covers acceptance criteria and read-back evidence.  - [Provenance and revision-pinned citations](/wiki/provenance-and-revision-pinned-citations) covers durable evidence identity.  - [Exponential backoff with jitter](/wiki/exponential-backoff-with-jitter) addresses retry pacing, which is separate from duplicate-effect safety.  - [Exactly-once delivery](/wiki/exactly-once-delivery) is the broader distributed-systems claim that an idempotency key only partially addresses.