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CONCEPT Cited by 1 source

Durable Streams

Definition

An append-only, immutable event log applied to LLM agent execution history. Every event — prompt, tool response, model choice — is recorded as an unchangeable ledger entry. If the agent process dies, a new instance picks up the log and continues from the exact step where execution was interrupted.

Introduced by Flue as its production crash-recovery mechanism. The concept applies distributed log / event-sourcing principles to the specific problem of agent-turn durability.

(Source: Agents platform post.)

Key properties

  • Append-only: no mutation of past entries; the log is the source of truth.
  • Immutable: each entry (prompt, response, choice) is unchangeable once written.
  • Resumable: any fresh instance can replay from the last checkpoint.
  • Agent-state never volatile: even if the process crashes mid-turn, state is reconstructable.

Relationship to fibers

Durable Streams operate at the framework level (Flue). At the runtime level, fibers (runFiber / stash / onFiberRecovered) provide the underlying checkpointing mechanism when deployed to Cloudflare.

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