[Bug] Cut height may not synchronize with consensus height

[qj0r9j0vc2]

Problem

There is a potential synchronization issue between the Cut heights produced by DCL and the heights requested by the consensus layer. If they don't match, build_value() will timeout waiting for a Cut that never arrives.

Location

• crates/consensus/src/host.rs:882-890 (cut storage)
• crates/consensus/src/host.rs:733-773 (build_value)

Code Analysis

Cut Storage (spawn_host)

// Spawn background task to process DCL cuts
tokio::spawn(async move {
    while let Some(cut) = cut_rx.recv().await {
        let height = ConsensusHeight::from(cut.height);  // Uses Cut's internal height
        value_builder_for_cuts.store_cut(height, cut).await;
    }
});

Value Request (build_value)

async fn build_value(
    &self,
    height: ConsensusHeight,  // Consensus's requested height
    _round: ConsensusRound,
) -> Result<LocallyProposedValue<CipherBftContext>, ConsensusError> {
    let timeout = Duration::from_secs(30);
    
    loop {
        {
            let mut pending = self.pending_cuts.write().await;
            if let Some(cut) = pending.remove(&height) {  // Looks up by consensus height
                // ...
            }
        }
        
        if start.elapsed() > timeout {
            return Err(ConsensusError::Other(format!(
                "Timeout: No cut available for height {} after {:?}",
                height, timeout
            )));
        }
        // ...
    }
}

The Issue

1. DCL Primary produces Cuts with cut.height set to some value
2. Cuts are stored by their internal height: store_cut(cut.height, cut)
3. Consensus requests values at its own height via build_value(consensus_height, _)
4. If cut.height != consensus_height, the lookup fails

Potential Causes

• DCL starts at height 1, consensus starts at height 1 - OK if synchronized
• If consensus restarts at height N but DCL is still at height M, mismatch occurs
• No explicit synchronization mechanism between DCL and consensus heights

Impact

• 30-second timeout on every round: If heights don't match, build_value spins for 30 seconds then fails
• Node appears stuck: Consensus cannot make progress
• Difficult to diagnose: Timeout error doesn't indicate the height mismatch

Suggested Fix

1. Explicit height synchronization: DCL should be informed of the current consensus height

// In Primary or CutFormer
pub fn set_consensus_height(&mut self, height: u64) {
    self.next_cut_height = height;
}

2. Better error messages: Include both requested and available heights

if start.elapsed() > timeout {
    let available: Vec<_> = self.pending_cuts.read().await.keys().collect();
    return Err(ConsensusError::Other(format!(
        "Timeout: No cut at height {}. Available heights: {:?}",
        height, available
    )));
}

3. Height validation: Warn when storing a Cut if the height seems off

pub async fn store_cut(&self, height: ConsensusHeight, cut: Cut) {
    if cut.height != height.0 {
        warn!("Cut internal height {} differs from storage height {}", cut.height, height);
    }
    // ...
}

Severity

Medium - Could cause liveness issues if DCL and consensus heights diverge.