Two Roads to Durable Agents: Replay vs. Snapshot#
AI Engineer Europe 2026 digest Program Wildcard pick 8–10 April 2026
Eric Allam — Trigger.dev
- Why: Durable execution for agents today means application-level replay with determinism constraints; OS-level process snapshot/restore is an alternative almost nobody in AI engineering is using — a genuinely different systems approach from the virtualization/checkpointing world.
- What: An honest comparison of the two durability models: replay (record every step, replay on recovery, code must be deterministic, can't capture everything a running process holds in memory) versus OS-level snapshot (freeze the entire process, free resources, restore exactly where it left off — no replay log, no determinism requirement, no step boundaries). Live demo on Trigger.dev: checkpoint mid-execution, suspend at zero cost while waiting on a human, resume from snapshot.
- How: OS-level process checkpoint/snapshot mechanics applied to agent processes, versus event-sourced replay.
- Where applicable: Long-running agent platforms; the snapshot approach depends on runtime checkpoint support (demoed on Trigger.dev, so vendor origin), and the honest where-each-breaks comparison is the real content.