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Every graph step stores a full snapshot of the conversation, nothing pruned old ones, and deleting a conversation left its thread behind (about 1.6 MB per checkpoint at 200 turns). After each turn, only the newest CHECKPOINT_KEEP_PER_THREAD (default 20) checkpoints of that thread are kept, plus their pending writes; state reads only use the newest, and pruning a 200-checkpoint thread takes about 2 ms. Deleting a conversation also deletes its thread, without failing the request if the checkpoint store errors. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>