CheckpointMetadata

The source of the checkpoint.

• "input": The checkpoint was created from an input to invoke/stream/batch.
• "loop": The checkpoint was created from inside the pregel loop.
• "update": The checkpoint was created from a manual state update.
• "fork": The checkpoint was created as a copy of another checkpoint.

The step number of the checkpoint.

-1 for the first "input" checkpoint. 0 for the first "loop" checkpoint. ... for the nth checkpoint afterwards.

The IDs of the parent checkpoints.

Mapping from checkpoint namespace to checkpoint ID.

The ID of the run that created this checkpoint.

Per-channel counters since the last _DeltaSnapshot was written.

Maps channel name -> (updates, supersteps):

• index 0 (updates): number of supersteps that wrote to this channel since its last snapshot blob.
• index 1 (supersteps): total supersteps elapsed since this channel's last snapshot, regardless of whether the channel was written.

A snapshot fires when EITHER updates >= ch.snapshot_frequency OR supersteps >= DELTA_MAX_SUPERSTEPS_SINCE_SNAPSHOT (system-wide bound, default 5000, env LANGGRAPH_DELTA_MAX_SUPERSTEPS_SINCE_SNAPSHOT). The supersteps bound prevents unbounded ancestor walks on threads where a delta channel exists but is no longer being updated.

Absent on threads that don't use delta channels. Persisted as a 2-element list in JSON (no native tuple).