fix(langgraph): treat DeltaChannel Overwrite as a hard reset in update()#7956
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Christian Bromann (christian-bromann) wants to merge 1 commit into
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DeltaChannel.update() kept writes ordered before an Overwrite within the same super-step, while replay_writes() dropped them, so reconstructing a thread from a checkpoint produced different state than the live run. Align update() with replay_writes() (drop everything up to and including the overwrite) so reload reproduces live state.
Quanzheng Long (longquanzheng)
approved these changes
Jun 17, 2026
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Summary
DeltaChannel.update()andreplay_writes()disagreed when a plain write was ordered before anOverwritein the same super-step (e.g. parallel fan-in /Send):update()kept the pre-overwrite write,replay_writes()dropped it. This broke the DeltaChannel invariant that reconstruction from a checkpoint reproduces the live state.update()to treatOverwriteas a hard reset — drop everything up to and including the overwrite, keep only writes that follow it — matchingreplay_writes().