IBC Packet Commitment Timeout Mismatch Across Variable Block-Time Chains

[JamesEjembi]

Problem Statement / Feature Objective

The IBC (Inter-Blockchain Communication) packet commitment timeout is calculated using the source chain's block time assumption. When sending packets to a chain with variable block times (e.g., 2-30s range), the timeout can expire prematurely on fast blocks or be excessively long on slow blocks, causing packet loss or settlement delays.

Technical Invariants & Bounds

• Timeout calculation: source_height + (timeout_delta / source_block_time).
• Block time variance tracking: rolling window of 100 blocks.
• Timeout delta: configurable 10-300s.
• Packet lifetime: max 1000 blocks on destination chain.
• Mismatch penalty: >5% timeouts due to misestimation triggers recalibration.

Codebase Navigation Guide

• src/cross-chain/ibc/packet-timeout.rs — timeout calculation.
• src/cross-chain/ibc/block-time-estimator.rs — block time estimation.
• src/cross-chain/ibc/packet-relayer.rs — packet relay logic.
• src/cross-chain/consensus/header-sync.rs — header synchronization.

Implementation Blueprint

1. In block-time-estimator.rs, maintain an exponential moving average (EMA) of block times with alpha = 0.3 over 100 blocks; also track the 95th percentile.
2. In packet-timeout.rs, compute timeout as source_height + ceil(timeout_delta / p95_block_time_ms) instead of using a fixed value.
3. Add a safety margin: multiply the estimated block count by 1.5 for the first 10 packets to a new chain until sufficient block time samples are collected.
4. In packet-relayer.rs, emit a PacketTimeoutMisestimation event when a packet times out but the destination chain is still at or below the estimated timeout height.
5. Unit test: simulate variable block times (2s average with spikes to 30s), verify packet timeout accuracy >95%.