When Besu is behind the CL head (e.g., during initial sync or after restart), desync-tolerance=0 prevents maru from sending any fork choice updates to Besu. This causes Besu to remain stuck at its current block. Increasing desync-tolerance to 100000 allows maru to continue sending blocks even when Besu is significantly behind, enabling it to catch up. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>